gcc/libgcc/config/libbid/bid_round.c

/* Copyright (C) 2007-2022 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */

/*****************************************************************************
 *
 *  BID64 encoding:
 * ****************************************
 *  63  62              53 52           0
 * |---|------------------|--------------|
 * | S |  Biased Exp (E)  |  Coeff (c)   |
 * |---|------------------|--------------|
 *
 * bias = 398
 * number = (-1)^s * 10^(E-398) * c
 * coefficient range - 0 to (2^53)-1
 * COEFF_MAX = 2^53-1 = 9007199254740991
 *
 *****************************************************************************
 *
 * BID128 encoding:
 *   1-bit sign
 *   14-bit biased exponent in [0x21, 0x3020] = [33, 12320]
 *         unbiased exponent in [-6176, 6111]; exponent bias = 6176
 *   113-bit unsigned binary integer coefficient (49-bit high + 64-bit low)
 *   Note: 10^34-1 ~ 2^112.945555... < 2^113 => coefficient fits in 113 bits
 *
 *   Note: assume invalid encodings are not passed to this function
 *
 * Round a number C with q decimal digits, represented as a binary integer
 * to q - x digits. Six different routines are provided for different values 
 * of q. The maximum value of q used in the library is q = 3 * P - 1 where 
 * P = 16 or P = 34 (so q <= 111 decimal digits). 
 * The partitioning is based on the following, where Kx is the scaled
 * integer representing the value of 10^(-x) rounded up to a number of bits
 * sufficient to ensure correct rounding:
 *
 * --------------------------------------------------------------------------
 * q    x           max. value of  a            max number      min. number 
 *                                              of bits in C    of bits in Kx
 * --------------------------------------------------------------------------
 *
 *                          GROUP 1: 64 bits
 *                          round64_2_18 ()
 *
 * 2    [1,1]       10^1 - 1 < 2^3.33            4              4
 * ...  ...         ...                         ...             ...
 * 18   [1,17]      10^18 - 1 < 2^59.80         60              61
 *
 *                        GROUP 2: 128 bits
 *                        round128_19_38 ()
 *
 * 19   [1,18]      10^19 - 1 < 2^63.11         64              65
 * 20   [1,19]      10^20 - 1 < 2^66.44         67              68
 * ...  ...         ...                         ...             ...
 * 38   [1,37]      10^38 - 1 < 2^126.24        127             128
 *
 *                        GROUP 3: 192 bits
 *                        round192_39_57 ()
 *
 * 39   [1,38]      10^39 - 1 < 2^129.56        130             131
 * ...  ...         ...                         ...             ...
 * 57   [1,56]      10^57 - 1 < 2^189.35        190             191
 *
 *                        GROUP 4: 256 bits
 *                        round256_58_76 ()
 *
 * 58   [1,57]      10^58 - 1 < 2^192.68        193             194
 * ...  ...         ...                         ...             ...
 * 76   [1,75]      10^76 - 1 < 2^252.47        253             254
 *
 *                        GROUP 5: 320 bits
 *                        round320_77_96 ()
 *
 * 77   [1,76]      10^77 - 1 < 2^255.79        256             257
 * 78   [1,77]      10^78 - 1 < 2^259.12        260             261
 * ...  ...         ...                         ...             ...
 * 96   [1,95]      10^96 - 1 < 2^318.91        319             320
 *
 *                        GROUP 6: 384 bits
 *                        round384_97_115 ()
 *
 * 97   [1,96]      10^97 - 1 < 2^322.23        323             324 
 * ...  ...         ...                         ...             ...
 * 115  [1,114]     10^115 - 1 < 2^382.03       383             384
 *
 ****************************************************************************/

#include "bid_internal.h"

void
round64_2_18 (int q,
	      int x,
	      UINT64 C,
	      UINT64 * ptr_Cstar,
	      int *incr_exp,
	      int *ptr_is_midpoint_lt_even,
	      int *ptr_is_midpoint_gt_even,
	      int *ptr_is_inexact_lt_midpoint,
	      int *ptr_is_inexact_gt_midpoint) {

  UINT128 P128;
  UINT128 fstar;
  UINT64 Cstar;
  UINT64 tmp64;
  int shift;
  int ind;

  // Note:
  //    In round128_2_18() positive numbers with 2 <= q <= 18 will be 
  //    rounded to nearest only for 1 <= x <= 3:
  //     x = 1 or x = 2 when q = 17
  //     x = 2 or x = 3 when q = 18
  // However, for generality and possible uses outside the frame of IEEE 754R
  // this implementation works for 1 <= x <= q - 1

  // assume *ptr_is_midpoint_lt_even, *ptr_is_midpoint_gt_even,
  // *ptr_is_inexact_lt_midpoint, and *ptr_is_inexact_gt_midpoint are
  // initialized to 0 by the caller

  // round a number C with q decimal digits, 2 <= q <= 18
  // to q - x digits, 1 <= x <= 17
  // C = C + 1/2 * 10^x where the result C fits in 64 bits
  // (because the largest value is 999999999999999999 + 50000000000000000 =
  // 0x0e92596fd628ffff, which fits in 60 bits)
  ind = x - 1;	// 0 <= ind <= 16
  C = C + midpoint64[ind];
  // kx ~= 10^(-x), kx = Kx64[ind] * 2^(-Ex), 0 <= ind <= 16
  // P128 = (C + 1/2 * 10^x) * kx * 2^Ex = (C + 1/2 * 10^x) * Kx
  // the approximation kx of 10^(-x) was rounded up to 64 bits
  __mul_64x64_to_128MACH (P128, C, Kx64[ind]);
  // calculate C* = floor (P128) and f*
  // Cstar = P128 >> Ex
  // fstar = low Ex bits of P128
  shift = Ex64m64[ind];	// in [3, 56]
  Cstar = P128.w[1] >> shift;
  fstar.w[1] = P128.w[1] & mask64[ind];
  fstar.w[0] = P128.w[0];
  // the top Ex bits of 10^(-x) are T* = ten2mxtrunc64[ind], e.g.
  // if x=1, T*=ten2mxtrunc64[0]=0xcccccccccccccccc
  // if (0 < f* < 10^(-x)) then the result is a midpoint
  //   if floor(C*) is even then C* = floor(C*) - logical right
  //       shift; C* has q - x decimal digits, correct by Prop. 1)
  //   else if floor(C*) is odd C* = floor(C*)-1 (logical right
  //       shift; C* has q - x decimal digits, correct by Pr. 1)
  // else
  //   C* = floor(C*) (logical right shift; C has q - x decimal digits,
  //       correct by Property 1)
  // in the caling function n = C* * 10^(e+x)

  // determine inexactness of the rounding of C*
  // if (0 < f* - 1/2 < 10^(-x)) then
  //   the result is exact
  // else // if (f* - 1/2 > T*) then
  //   the result is inexact
  if (fstar.w[1] > half64[ind] ||
      (fstar.w[1] == half64[ind] && fstar.w[0])) {
    // f* > 1/2 and the result may be exact
    // Calculate f* - 1/2
    tmp64 = fstar.w[1] - half64[ind];
    if (tmp64 || fstar.w[0] > ten2mxtrunc64[ind]) {	// f* - 1/2 > 10^(-x)
      *ptr_is_inexact_lt_midpoint = 1;
    }	// else the result is exact
  } else {	// the result is inexact; f2* <= 1/2
    *ptr_is_inexact_gt_midpoint = 1;
  }
  // check for midpoints (could do this before determining inexactness)
  if (fstar.w[1] == 0 && fstar.w[0] <= ten2mxtrunc64[ind]) {
    // the result is a midpoint
    if (Cstar & 0x01) {	// Cstar is odd; MP in [EVEN, ODD]
      // if floor(C*) is odd C = floor(C*) - 1; the result may be 0
      Cstar--;	// Cstar is now even
      *ptr_is_midpoint_gt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    } else {	// else MP in [ODD, EVEN]
      *ptr_is_midpoint_lt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    }
  }
  // check for rounding overflow, which occurs if Cstar = 10^(q-x)
  ind = q - x;	// 1 <= ind <= q - 1
  if (Cstar == ten2k64[ind]) {	// if  Cstar = 10^(q-x)
    Cstar = ten2k64[ind - 1];	// Cstar = 10^(q-x-1)
    *incr_exp = 1;
  } else {	// 10^33 <= Cstar <= 10^34 - 1
    *incr_exp = 0;
  }
  *ptr_Cstar = Cstar;
}


void
round128_19_38 (int q,
		int x,
		UINT128 C,
		UINT128 * ptr_Cstar,
		int *incr_exp,
		int *ptr_is_midpoint_lt_even,
		int *ptr_is_midpoint_gt_even,
		int *ptr_is_inexact_lt_midpoint,
		int *ptr_is_inexact_gt_midpoint) {

  UINT256 P256;
  UINT256 fstar;
  UINT128 Cstar;
  UINT64 tmp64;
  int shift;
  int ind;

  // Note:
  //    In round128_19_38() positive numbers with 19 <= q <= 38 will be 
  //    rounded to nearest only for 1 <= x <= 23:
  //     x = 3 or x = 4 when q = 19
  //     x = 4 or x = 5 when q = 20
  //     ...
  //     x = 18 or x = 19 when q = 34
  //     x = 1 or x = 2 or x = 19 or x = 20 when q = 35
  //     x = 2 or x = 3 or x = 20 or x = 21 when q = 36
  //     x = 3 or x = 4 or x = 21 or x = 22 when q = 37
  //     x = 4 or x = 5 or x = 22 or x = 23 when q = 38
  // However, for generality and possible uses outside the frame of IEEE 754R
  // this implementation works for 1 <= x <= q - 1

  // assume *ptr_is_midpoint_lt_even, *ptr_is_midpoint_gt_even,
  // *ptr_is_inexact_lt_midpoint, and *ptr_is_inexact_gt_midpoint are
  // initialized to 0 by the caller

  // round a number C with q decimal digits, 19 <= q <= 38
  // to q - x digits, 1 <= x <= 37
  // C = C + 1/2 * 10^x where the result C fits in 128 bits
  // (because the largest value is 99999999999999999999999999999999999999 + 
  // 5000000000000000000000000000000000000 =
  // 0x4efe43b0c573e7e68a043d8fffffffff, which fits is 127 bits)

  ind = x - 1;	// 0 <= ind <= 36 
  if (ind <= 18) {	// if 0 <= ind <= 18
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint64[ind];
    if (C.w[0] < tmp64)
      C.w[1]++;
  } else {	// if 19 <= ind <= 37
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint128[ind - 19].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
    }
    C.w[1] = C.w[1] + midpoint128[ind - 19].w[1];
  }
  // kx ~= 10^(-x), kx = Kx128[ind] * 2^(-Ex), 0 <= ind <= 36
  // P256 = (C + 1/2 * 10^x) * kx * 2^Ex = (C + 1/2 * 10^x) * Kx
  // the approximation kx of 10^(-x) was rounded up to 128 bits
  __mul_128x128_to_256 (P256, C, Kx128[ind]);
  // calculate C* = floor (P256) and f*
  // Cstar = P256 >> Ex
  // fstar = low Ex bits of P256
  shift = Ex128m128[ind];	// in [2, 63] but have to consider two cases
  if (ind <= 18) {	// if 0 <= ind <= 18 
    Cstar.w[0] = (P256.w[2] >> shift) | (P256.w[3] << (64 - shift));
    Cstar.w[1] = (P256.w[3] >> shift);
    fstar.w[0] = P256.w[0];
    fstar.w[1] = P256.w[1];
    fstar.w[2] = P256.w[2] & mask128[ind];
    fstar.w[3] = 0x0ULL;
  } else {	// if 19 <= ind <= 37
    Cstar.w[0] = P256.w[3] >> shift;
    Cstar.w[1] = 0x0ULL;
    fstar.w[0] = P256.w[0];
    fstar.w[1] = P256.w[1];
    fstar.w[2] = P256.w[2];
    fstar.w[3] = P256.w[3] & mask128[ind];
  }
  // the top Ex bits of 10^(-x) are T* = ten2mxtrunc64[ind], e.g.
  // if x=1, T*=ten2mxtrunc128[0]=0xcccccccccccccccccccccccccccccccc
  // if (0 < f* < 10^(-x)) then the result is a midpoint
  //   if floor(C*) is even then C* = floor(C*) - logical right
  //       shift; C* has q - x decimal digits, correct by Prop. 1)
  //   else if floor(C*) is odd C* = floor(C*)-1 (logical right
  //       shift; C* has q - x decimal digits, correct by Pr. 1)
  // else
  //   C* = floor(C*) (logical right shift; C has q - x decimal digits,
  //       correct by Property 1)
  // in the caling function n = C* * 10^(e+x)

  // determine inexactness of the rounding of C*
  // if (0 < f* - 1/2 < 10^(-x)) then
  //   the result is exact
  // else // if (f* - 1/2 > T*) then
  //   the result is inexact
  if (ind <= 18) {	// if 0 <= ind <= 18
    if (fstar.w[2] > half128[ind] ||
	(fstar.w[2] == half128[ind] && (fstar.w[1] || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[2] - half128[ind];
      if (tmp64 || fstar.w[1] > ten2mxtrunc128[ind].w[1] || (fstar.w[1] == ten2mxtrunc128[ind].w[1] && fstar.w[0] > ten2mxtrunc128[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else {	// if 19 <= ind <= 37
    if (fstar.w[3] > half128[ind] || (fstar.w[3] == half128[ind] &&
				      (fstar.w[2] || fstar.w[1]
				       || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[3] - half128[ind];
      if (tmp64 || fstar.w[2] || fstar.w[1] > ten2mxtrunc128[ind].w[1] || (fstar.w[1] == ten2mxtrunc128[ind].w[1] && fstar.w[0] > ten2mxtrunc128[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  }
  // check for midpoints (could do this before determining inexactness)
  if (fstar.w[3] == 0 && fstar.w[2] == 0 &&
      (fstar.w[1] < ten2mxtrunc128[ind].w[1] ||
       (fstar.w[1] == ten2mxtrunc128[ind].w[1] &&
	fstar.w[0] <= ten2mxtrunc128[ind].w[0]))) {
    // the result is a midpoint
    if (Cstar.w[0] & 0x01) {	// Cstar is odd; MP in [EVEN, ODD]
      // if floor(C*) is odd C = floor(C*) - 1; the result may be 0
      Cstar.w[0]--;	// Cstar is now even
      if (Cstar.w[0] == 0xffffffffffffffffULL) {
	Cstar.w[1]--;
      }
      *ptr_is_midpoint_gt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    } else {	// else MP in [ODD, EVEN]
      *ptr_is_midpoint_lt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    }
  }
  // check for rounding overflow, which occurs if Cstar = 10^(q-x)
  ind = q - x;	// 1 <= ind <= q - 1
  if (ind <= 19) {
    if (Cstar.w[1] == 0x0ULL && Cstar.w[0] == ten2k64[ind]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[ind - 1];	// Cstar = 10^(q-x-1)
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind == 20) {
    // if ind = 20
    if (Cstar.w[1] == ten2k128[0].w[1]
	&& Cstar.w[0] == ten2k128[0].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[19];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = 0x0ULL;
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else {	// if 21 <= ind <= 37
    if (Cstar.w[1] == ten2k128[ind - 20].w[1] &&
	Cstar.w[0] == ten2k128[ind - 20].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k128[ind - 21].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k128[ind - 21].w[1];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  }
  ptr_Cstar->w[1] = Cstar.w[1];
  ptr_Cstar->w[0] = Cstar.w[0];
}


void
round192_39_57 (int q,
		int x,
		UINT192 C,
		UINT192 * ptr_Cstar,
		int *incr_exp,
		int *ptr_is_midpoint_lt_even,
		int *ptr_is_midpoint_gt_even,
		int *ptr_is_inexact_lt_midpoint,
		int *ptr_is_inexact_gt_midpoint) {

  UINT384 P384;
  UINT384 fstar;
  UINT192 Cstar;
  UINT64 tmp64;
  int shift;
  int ind;

  // Note:
  //    In round192_39_57() positive numbers with 39 <= q <= 57 will be 
  //    rounded to nearest only for 5 <= x <= 42:
  //     x = 23 or x = 24 or x = 5 or x = 6 when q = 39
  //     x = 24 or x = 25 or x = 6 or x = 7 when q = 40
  //     ...
  //     x = 41 or x = 42 or x = 23 or x = 24 when q = 57
  // However, for generality and possible uses outside the frame of IEEE 754R
  // this implementation works for 1 <= x <= q - 1

  // assume *ptr_is_midpoint_lt_even, *ptr_is_midpoint_gt_even,
  // *ptr_is_inexact_lt_midpoint, and *ptr_is_inexact_gt_midpoint are
  // initialized to 0 by the caller

  // round a number C with q decimal digits, 39 <= q <= 57
  // to q - x digits, 1 <= x <= 56
  // C = C + 1/2 * 10^x where the result C fits in 192 bits
  // (because the largest value is
  // 999999999999999999999999999999999999999999999999999999999 +
  //  50000000000000000000000000000000000000000000000000000000 =
  // 0x2ad282f212a1da846afdaf18c034ff09da7fffffffffffff, which fits in 190 bits)
  ind = x - 1;	// 0 <= ind <= 55
  if (ind <= 18) {	// if 0 <= ind <= 18
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint64[ind];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0) {
	C.w[2]++;
      }
    }
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint128[ind - 19].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0) {
	C.w[2]++;
      }
    }
    tmp64 = C.w[1];
    C.w[1] = C.w[1] + midpoint128[ind - 19].w[1];
    if (C.w[1] < tmp64) {
      C.w[2]++;
    }
  } else {	// if 38 <= ind <= 57 (actually ind <= 55)
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint192[ind - 38].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0ull) {
	C.w[2]++;
      }
    }
    tmp64 = C.w[1];
    C.w[1] = C.w[1] + midpoint192[ind - 38].w[1];
    if (C.w[1] < tmp64) {
      C.w[2]++;
    }
    C.w[2] = C.w[2] + midpoint192[ind - 38].w[2];
  }
  // kx ~= 10^(-x), kx = Kx192[ind] * 2^(-Ex), 0 <= ind <= 55
  // P384 = (C + 1/2 * 10^x) * kx * 2^Ex = (C + 1/2 * 10^x) * Kx
  // the approximation kx of 10^(-x) was rounded up to 192 bits
  __mul_192x192_to_384 (P384, C, Kx192[ind]);
  // calculate C* = floor (P384) and f*
  // Cstar = P384 >> Ex
  // fstar = low Ex bits of P384
  shift = Ex192m192[ind];	// in [1, 63] but have to consider three cases
  if (ind <= 18) {	// if 0 <= ind <= 18 
    Cstar.w[2] = (P384.w[5] >> shift);
    Cstar.w[1] = (P384.w[5] << (64 - shift)) | (P384.w[4] >> shift);
    Cstar.w[0] = (P384.w[4] << (64 - shift)) | (P384.w[3] >> shift);
    fstar.w[5] = 0x0ULL;
    fstar.w[4] = 0x0ULL;
    fstar.w[3] = P384.w[3] & mask192[ind];
    fstar.w[2] = P384.w[2];
    fstar.w[1] = P384.w[1];
    fstar.w[0] = P384.w[0];
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    Cstar.w[2] = 0x0ULL;
    Cstar.w[1] = P384.w[5] >> shift;
    Cstar.w[0] = (P384.w[5] << (64 - shift)) | (P384.w[4] >> shift);
    fstar.w[5] = 0x0ULL;
    fstar.w[4] = P384.w[4] & mask192[ind];
    fstar.w[3] = P384.w[3];
    fstar.w[2] = P384.w[2];
    fstar.w[1] = P384.w[1];
    fstar.w[0] = P384.w[0];
  } else {	// if 38 <= ind <= 57
    Cstar.w[2] = 0x0ULL;
    Cstar.w[1] = 0x0ULL;
    Cstar.w[0] = P384.w[5] >> shift;
    fstar.w[5] = P384.w[5] & mask192[ind];
    fstar.w[4] = P384.w[4];
    fstar.w[3] = P384.w[3];
    fstar.w[2] = P384.w[2];
    fstar.w[1] = P384.w[1];
    fstar.w[0] = P384.w[0];
  }

  // the top Ex bits of 10^(-x) are T* = ten2mxtrunc192[ind], e.g. if x=1,
  // T*=ten2mxtrunc192[0]=0xcccccccccccccccccccccccccccccccccccccccccccccccc
  // if (0 < f* < 10^(-x)) then the result is a midpoint
  //   if floor(C*) is even then C* = floor(C*) - logical right
  //       shift; C* has q - x decimal digits, correct by Prop. 1)
  //   else if floor(C*) is odd C* = floor(C*)-1 (logical right
  //       shift; C* has q - x decimal digits, correct by Pr. 1)
  // else
  //   C* = floor(C*) (logical right shift; C has q - x decimal digits,
  //       correct by Property 1)
  // in the caling function n = C* * 10^(e+x)

  // determine inexactness of the rounding of C*
  // if (0 < f* - 1/2 < 10^(-x)) then
  //   the result is exact
  // else // if (f* - 1/2 > T*) then
  //   the result is inexact
  if (ind <= 18) {	// if 0 <= ind <= 18
    if (fstar.w[3] > half192[ind] || (fstar.w[3] == half192[ind] &&
				      (fstar.w[2] || fstar.w[1]
				       || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[3] - half192[ind];
      if (tmp64 || fstar.w[2] > ten2mxtrunc192[ind].w[2] || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] > ten2mxtrunc192[ind].w[1]) || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] == ten2mxtrunc192[ind].w[1] && fstar.w[0] > ten2mxtrunc192[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    if (fstar.w[4] > half192[ind] || (fstar.w[4] == half192[ind] &&
				      (fstar.w[3] || fstar.w[2]
				       || fstar.w[1] || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[4] - half192[ind];
      if (tmp64 || fstar.w[3] || fstar.w[2] > ten2mxtrunc192[ind].w[2] || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] > ten2mxtrunc192[ind].w[1]) || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] == ten2mxtrunc192[ind].w[1] && fstar.w[0] > ten2mxtrunc192[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else {	// if 38 <= ind <= 55
    if (fstar.w[5] > half192[ind] || (fstar.w[5] == half192[ind] &&
				      (fstar.w[4] || fstar.w[3]
				       || fstar.w[2] || fstar.w[1]
				       || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[5] - half192[ind];
      if (tmp64 || fstar.w[4] || fstar.w[3] || fstar.w[2] > ten2mxtrunc192[ind].w[2] || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] > ten2mxtrunc192[ind].w[1]) || (fstar.w[2] == ten2mxtrunc192[ind].w[2] && fstar.w[1] == ten2mxtrunc192[ind].w[1] && fstar.w[0] > ten2mxtrunc192[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  }
  // check for midpoints (could do this before determining inexactness)
  if (fstar.w[5] == 0 && fstar.w[4] == 0 && fstar.w[3] == 0 &&
      (fstar.w[2] < ten2mxtrunc192[ind].w[2] ||
       (fstar.w[2] == ten2mxtrunc192[ind].w[2] &&
	fstar.w[1] < ten2mxtrunc192[ind].w[1]) ||
       (fstar.w[2] == ten2mxtrunc192[ind].w[2] &&
	fstar.w[1] == ten2mxtrunc192[ind].w[1] &&
	fstar.w[0] <= ten2mxtrunc192[ind].w[0]))) {
    // the result is a midpoint
    if (Cstar.w[0] & 0x01) {	// Cstar is odd; MP in [EVEN, ODD]
      // if floor(C*) is odd C = floor(C*) - 1; the result may be 0
      Cstar.w[0]--;	// Cstar is now even
      if (Cstar.w[0] == 0xffffffffffffffffULL) {
	Cstar.w[1]--;
	if (Cstar.w[1] == 0xffffffffffffffffULL) {
	  Cstar.w[2]--;
	}
      }
      *ptr_is_midpoint_gt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    } else {	// else MP in [ODD, EVEN]
      *ptr_is_midpoint_lt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    }
  }
  // check for rounding overflow, which occurs if Cstar = 10^(q-x)
  ind = q - x;	// 1 <= ind <= q - 1
  if (ind <= 19) {
    if (Cstar.w[2] == 0x0ULL && Cstar.w[1] == 0x0ULL &&
	Cstar.w[0] == ten2k64[ind]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[ind - 1];	// Cstar = 10^(q-x-1)
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind == 20) {
    // if ind = 20
    if (Cstar.w[2] == 0x0ULL && Cstar.w[1] == ten2k128[0].w[1] &&
	Cstar.w[0] == ten2k128[0].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[19];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = 0x0ULL;
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind <= 38) {	// if 21 <= ind <= 38
    if (Cstar.w[2] == 0x0ULL && Cstar.w[1] == ten2k128[ind - 20].w[1] &&
	Cstar.w[0] == ten2k128[ind - 20].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k128[ind - 21].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k128[ind - 21].w[1];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind == 39) {
    if (Cstar.w[2] == ten2k256[0].w[2] && Cstar.w[1] == ten2k256[0].w[1]
	&& Cstar.w[0] == ten2k256[0].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k128[18].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k128[18].w[1];
      Cstar.w[2] = 0x0ULL;
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else {	// if 40 <= ind <= 56
    if (Cstar.w[2] == ten2k256[ind - 39].w[2] &&
	Cstar.w[1] == ten2k256[ind - 39].w[1] &&
	Cstar.w[0] == ten2k256[ind - 39].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k256[ind - 40].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k256[ind - 40].w[1];
      Cstar.w[2] = ten2k256[ind - 40].w[2];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  }
  ptr_Cstar->w[2] = Cstar.w[2];
  ptr_Cstar->w[1] = Cstar.w[1];
  ptr_Cstar->w[0] = Cstar.w[0];
}


void
round256_58_76 (int q,
		int x,
		UINT256 C,
		UINT256 * ptr_Cstar,
		int *incr_exp,
		int *ptr_is_midpoint_lt_even,
		int *ptr_is_midpoint_gt_even,
		int *ptr_is_inexact_lt_midpoint,
		int *ptr_is_inexact_gt_midpoint) {

  UINT512 P512;
  UINT512 fstar;
  UINT256 Cstar;
  UINT64 tmp64;
  int shift;
  int ind;

  // Note:
  //    In round256_58_76() positive numbers with 58 <= q <= 76 will be 
  //    rounded to nearest only for 24 <= x <= 61:
  //     x = 42 or x = 43 or x = 24 or x = 25 when q = 58
  //     x = 43 or x = 44 or x = 25 or x = 26 when q = 59
  //     ...
  //     x = 60 or x = 61 or x = 42 or x = 43 when q = 76
  // However, for generality and possible uses outside the frame of IEEE 754R
  // this implementation works for 1 <= x <= q - 1

  // assume *ptr_is_midpoint_lt_even, *ptr_is_midpoint_gt_even,
  // *ptr_is_inexact_lt_midpoint, and *ptr_is_inexact_gt_midpoint are
  // initialized to 0 by the caller

  // round a number C with q decimal digits, 58 <= q <= 76
  // to q - x digits, 1 <= x <= 75
  // C = C + 1/2 * 10^x where the result C fits in 256 bits
  // (because the largest value is 9999999999999999999999999999999999999999
  //     999999999999999999999999999999999999 + 500000000000000000000000000
  //     000000000000000000000000000000000000000000000000 =
  //     0x1736ca15d27a56cae15cf0e7b403d1f2bd6ebb0a50dc83ffffffffffffffffff, 
  // which fits in 253 bits)
  ind = x - 1;	// 0 <= ind <= 74
  if (ind <= 18) {	// if 0 <= ind <= 18
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint64[ind];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0) {
	C.w[2]++;
	if (C.w[2] == 0x0) {
	  C.w[3]++;
	}
      }
    }
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint128[ind - 19].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0) {
	C.w[2]++;
	if (C.w[2] == 0x0) {
	  C.w[3]++;
	}
      }
    }
    tmp64 = C.w[1];
    C.w[1] = C.w[1] + midpoint128[ind - 19].w[1];
    if (C.w[1] < tmp64) {
      C.w[2]++;
      if (C.w[2] == 0x0) {
	C.w[3]++;
      }
    }
  } else if (ind <= 57) {	// if 38 <= ind <= 57
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint192[ind - 38].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0ull) {
	C.w[2]++;
	if (C.w[2] == 0x0) {
	  C.w[3]++;
	}
      }
    }
    tmp64 = C.w[1];
    C.w[1] = C.w[1] + midpoint192[ind - 38].w[1];
    if (C.w[1] < tmp64) {
      C.w[2]++;
      if (C.w[2] == 0x0) {
	C.w[3]++;
      }
    }
    tmp64 = C.w[2];
    C.w[2] = C.w[2] + midpoint192[ind - 38].w[2];
    if (C.w[2] < tmp64) {
      C.w[3]++;
    }
  } else {	// if 58 <= ind <= 76 (actually 58 <= ind <= 74)
    tmp64 = C.w[0];
    C.w[0] = C.w[0] + midpoint256[ind - 58].w[0];
    if (C.w[0] < tmp64) {
      C.w[1]++;
      if (C.w[1] == 0x0ull) {
	C.w[2]++;
	if (C.w[2] == 0x0) {
	  C.w[3]++;
	}
      }
    }
    tmp64 = C.w[1];
    C.w[1] = C.w[1] + midpoint256[ind - 58].w[1];
    if (C.w[1] < tmp64) {
      C.w[2]++;
      if (C.w[2] == 0x0) {
	C.w[3]++;
      }
    }
    tmp64 = C.w[2];
    C.w[2] = C.w[2] + midpoint256[ind - 58].w[2];
    if (C.w[2] < tmp64) {
      C.w[3]++;
    }
    C.w[3] = C.w[3] + midpoint256[ind - 58].w[3];
  }
  // kx ~= 10^(-x), kx = Kx256[ind] * 2^(-Ex), 0 <= ind <= 74
  // P512 = (C + 1/2 * 10^x) * kx * 2^Ex = (C + 1/2 * 10^x) * Kx
  // the approximation kx of 10^(-x) was rounded up to 192 bits
  __mul_256x256_to_512 (P512, C, Kx256[ind]);
  // calculate C* = floor (P512) and f*
  // Cstar = P512 >> Ex
  // fstar = low Ex bits of P512
  shift = Ex256m256[ind];	// in [0, 63] but have to consider four cases
  if (ind <= 18) {	// if 0 <= ind <= 18 
    Cstar.w[3] = (P512.w[7] >> shift);
    Cstar.w[2] = (P512.w[7] << (64 - shift)) | (P512.w[6] >> shift);
    Cstar.w[1] = (P512.w[6] << (64 - shift)) | (P512.w[5] >> shift);
    Cstar.w[0] = (P512.w[5] << (64 - shift)) | (P512.w[4] >> shift);
    fstar.w[7] = 0x0ULL;
    fstar.w[6] = 0x0ULL;
    fstar.w[5] = 0x0ULL;
    fstar.w[4] = P512.w[4] & mask256[ind];
    fstar.w[3] = P512.w[3];
    fstar.w[2] = P512.w[2];
    fstar.w[1] = P512.w[1];
    fstar.w[0] = P512.w[0];
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    Cstar.w[3] = 0x0ULL;
    Cstar.w[2] = P512.w[7] >> shift;
    Cstar.w[1] = (P512.w[7] << (64 - shift)) | (P512.w[6] >> shift);
    Cstar.w[0] = (P512.w[6] << (64 - shift)) | (P512.w[5] >> shift);
    fstar.w[7] = 0x0ULL;
    fstar.w[6] = 0x0ULL;
    fstar.w[5] = P512.w[5] & mask256[ind];
    fstar.w[4] = P512.w[4];
    fstar.w[3] = P512.w[3];
    fstar.w[2] = P512.w[2];
    fstar.w[1] = P512.w[1];
    fstar.w[0] = P512.w[0];
  } else if (ind <= 56) {	// if 38 <= ind <= 56
    Cstar.w[3] = 0x0ULL;
    Cstar.w[2] = 0x0ULL;
    Cstar.w[1] = P512.w[7] >> shift;
    Cstar.w[0] = (P512.w[7] << (64 - shift)) | (P512.w[6] >> shift);
    fstar.w[7] = 0x0ULL;
    fstar.w[6] = P512.w[6] & mask256[ind];
    fstar.w[5] = P512.w[5];
    fstar.w[4] = P512.w[4];
    fstar.w[3] = P512.w[3];
    fstar.w[2] = P512.w[2];
    fstar.w[1] = P512.w[1];
    fstar.w[0] = P512.w[0];
  } else if (ind == 57) {
    Cstar.w[3] = 0x0ULL;
    Cstar.w[2] = 0x0ULL;
    Cstar.w[1] = 0x0ULL;
    Cstar.w[0] = P512.w[7];
    fstar.w[7] = 0x0ULL;
    fstar.w[6] = P512.w[6];
    fstar.w[5] = P512.w[5];
    fstar.w[4] = P512.w[4];
    fstar.w[3] = P512.w[3];
    fstar.w[2] = P512.w[2];
    fstar.w[1] = P512.w[1];
    fstar.w[0] = P512.w[0];
  } else {	// if 58 <= ind <= 74
    Cstar.w[3] = 0x0ULL;
    Cstar.w[2] = 0x0ULL;
    Cstar.w[1] = 0x0ULL;
    Cstar.w[0] = P512.w[7] >> shift;
    fstar.w[7] = P512.w[7] & mask256[ind];
    fstar.w[6] = P512.w[6];
    fstar.w[5] = P512.w[5];
    fstar.w[4] = P512.w[4];
    fstar.w[3] = P512.w[3];
    fstar.w[2] = P512.w[2];
    fstar.w[1] = P512.w[1];
    fstar.w[0] = P512.w[0];
  }

  // the top Ex bits of 10^(-x) are T* = ten2mxtrunc256[ind], e.g. if x=1,
  // T*=ten2mxtrunc256[0]=
  //     0xcccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
  // if (0 < f* < 10^(-x)) then the result is a midpoint
  //   if floor(C*) is even then C* = floor(C*) - logical right
  //       shift; C* has q - x decimal digits, correct by Prop. 1)
  //   else if floor(C*) is odd C* = floor(C*)-1 (logical right
  //       shift; C* has q - x decimal digits, correct by Pr. 1)
  // else
  //   C* = floor(C*) (logical right shift; C has q - x decimal digits,
  //       correct by Property 1)
  // in the caling function n = C* * 10^(e+x)

  // determine inexactness of the rounding of C*
  // if (0 < f* - 1/2 < 10^(-x)) then
  //   the result is exact
  // else // if (f* - 1/2 > T*) then
  //   the result is inexact
  if (ind <= 18) {	// if 0 <= ind <= 18
    if (fstar.w[4] > half256[ind] || (fstar.w[4] == half256[ind] &&
				      (fstar.w[3] || fstar.w[2]
				       || fstar.w[1] || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[4] - half256[ind];
      if (tmp64 || fstar.w[3] > ten2mxtrunc256[ind].w[2] || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] > ten2mxtrunc256[ind].w[2]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] > ten2mxtrunc256[ind].w[1]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] == ten2mxtrunc256[ind].w[1] && fstar.w[0] > ten2mxtrunc256[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else if (ind <= 37) {	// if 19 <= ind <= 37
    if (fstar.w[5] > half256[ind] || (fstar.w[5] == half256[ind] &&
				      (fstar.w[4] || fstar.w[3]
				       || fstar.w[2] || fstar.w[1]
				       || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[5] - half256[ind];
      if (tmp64 || fstar.w[4] || fstar.w[3] > ten2mxtrunc256[ind].w[3] || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] > ten2mxtrunc256[ind].w[2]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] > ten2mxtrunc256[ind].w[1]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] == ten2mxtrunc256[ind].w[1] && fstar.w[0] > ten2mxtrunc256[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else if (ind <= 57) {	// if 38 <= ind <= 57
    if (fstar.w[6] > half256[ind] || (fstar.w[6] == half256[ind] &&
				      (fstar.w[5] || fstar.w[4]
				       || fstar.w[3] || fstar.w[2]
				       || fstar.w[1] || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[6] - half256[ind];
      if (tmp64 || fstar.w[5] || fstar.w[4] || fstar.w[3] > ten2mxtrunc256[ind].w[3] || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] > ten2mxtrunc256[ind].w[2]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] > ten2mxtrunc256[ind].w[1]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] == ten2mxtrunc256[ind].w[1] && fstar.w[0] > ten2mxtrunc256[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  } else {	// if 58 <= ind <= 74
    if (fstar.w[7] > half256[ind] || (fstar.w[7] == half256[ind] &&
				      (fstar.w[6] || fstar.w[5]
				       || fstar.w[4] || fstar.w[3]
				       || fstar.w[2] || fstar.w[1]
				       || fstar.w[0]))) {
      // f* > 1/2 and the result may be exact
      // Calculate f* - 1/2
      tmp64 = fstar.w[7] - half256[ind];
      if (tmp64 || fstar.w[6] || fstar.w[5] || fstar.w[4] || fstar.w[3] > ten2mxtrunc256[ind].w[3] || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] > ten2mxtrunc256[ind].w[2]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] > ten2mxtrunc256[ind].w[1]) || (fstar.w[3] == ten2mxtrunc256[ind].w[3] && fstar.w[2] == ten2mxtrunc256[ind].w[2] && fstar.w[1] == ten2mxtrunc256[ind].w[1] && fstar.w[0] > ten2mxtrunc256[ind].w[0])) {	// f* - 1/2 > 10^(-x)
	*ptr_is_inexact_lt_midpoint = 1;
      }	// else the result is exact
    } else {	// the result is inexact; f2* <= 1/2
      *ptr_is_inexact_gt_midpoint = 1;
    }
  }
  // check for midpoints (could do this before determining inexactness)
  if (fstar.w[7] == 0 && fstar.w[6] == 0 &&
      fstar.w[5] == 0 && fstar.w[4] == 0 &&
      (fstar.w[3] < ten2mxtrunc256[ind].w[3] ||
       (fstar.w[3] == ten2mxtrunc256[ind].w[3] &&
	fstar.w[2] < ten2mxtrunc256[ind].w[2]) ||
       (fstar.w[3] == ten2mxtrunc256[ind].w[3] &&
	fstar.w[2] == ten2mxtrunc256[ind].w[2] &&
	fstar.w[1] < ten2mxtrunc256[ind].w[1]) ||
       (fstar.w[3] == ten2mxtrunc256[ind].w[3] &&
	fstar.w[2] == ten2mxtrunc256[ind].w[2] &&
	fstar.w[1] == ten2mxtrunc256[ind].w[1] &&
	fstar.w[0] <= ten2mxtrunc256[ind].w[0]))) {
    // the result is a midpoint
    if (Cstar.w[0] & 0x01) {	// Cstar is odd; MP in [EVEN, ODD]
      // if floor(C*) is odd C = floor(C*) - 1; the result may be 0
      Cstar.w[0]--;	// Cstar is now even
      if (Cstar.w[0] == 0xffffffffffffffffULL) {
	Cstar.w[1]--;
	if (Cstar.w[1] == 0xffffffffffffffffULL) {
	  Cstar.w[2]--;
	  if (Cstar.w[2] == 0xffffffffffffffffULL) {
	    Cstar.w[3]--;
	  }
	}
      }
      *ptr_is_midpoint_gt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    } else {	// else MP in [ODD, EVEN]
      *ptr_is_midpoint_lt_even = 1;
      *ptr_is_inexact_lt_midpoint = 0;
      *ptr_is_inexact_gt_midpoint = 0;
    }
  }
  // check for rounding overflow, which occurs if Cstar = 10^(q-x)
  ind = q - x;	// 1 <= ind <= q - 1
  if (ind <= 19) {
    if (Cstar.w[3] == 0x0ULL && Cstar.w[2] == 0x0ULL &&
	Cstar.w[1] == 0x0ULL && Cstar.w[0] == ten2k64[ind]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[ind - 1];	// Cstar = 10^(q-x-1)
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind == 20) {
    // if ind = 20
    if (Cstar.w[3] == 0x0ULL && Cstar.w[2] == 0x0ULL &&
	Cstar.w[1] == ten2k128[0].w[1]
	&& Cstar.w[0] == ten2k128[0].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k64[19];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = 0x0ULL;
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind <= 38) {	// if 21 <= ind <= 38
    if (Cstar.w[3] == 0x0ULL && Cstar.w[2] == 0x0ULL &&
	Cstar.w[1] == ten2k128[ind - 20].w[1] &&
	Cstar.w[0] == ten2k128[ind - 20].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k128[ind - 21].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k128[ind - 21].w[1];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind == 39) {
    if (Cstar.w[3] == 0x0ULL && Cstar.w[2] == ten2k256[0].w[2] &&
	Cstar.w[1] == ten2k256[0].w[1]
	&& Cstar.w[0] == ten2k256[0].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k128[18].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k128[18].w[1];
      Cstar.w[2] = 0x0ULL;
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  } else if (ind <= 57) {	// if 40 <= ind <= 57
    if (Cstar.w[3] == 0x0ULL && Cstar.w[2] == ten2k256[ind - 39].w[2] &&
	Cstar.w[1] == ten2k256[ind - 39].w[1] &&
	Cstar.w[0] == ten2k256[ind - 39].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k256[ind - 40].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k256[ind - 40].w[1];
      Cstar.w[2] = ten2k256[ind - 40].w[2];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
    // else if (ind == 58) is not needed becauae we do not have ten2k192[] yet
  } else {	// if 58 <= ind <= 77 (actually 58 <= ind <= 74)
    if (Cstar.w[3] == ten2k256[ind - 39].w[3] &&
	Cstar.w[2] == ten2k256[ind - 39].w[2] &&
	Cstar.w[1] == ten2k256[ind - 39].w[1] &&
	Cstar.w[0] == ten2k256[ind - 39].w[0]) {
      // if  Cstar = 10^(q-x)
      Cstar.w[0] = ten2k256[ind - 40].w[0];	// Cstar = 10^(q-x-1)
      Cstar.w[1] = ten2k256[ind - 40].w[1];
      Cstar.w[2] = ten2k256[ind - 40].w[2];
      Cstar.w[3] = ten2k256[ind - 40].w[3];
      *incr_exp = 1;
    } else {
      *incr_exp = 0;
    }
  }
  ptr_Cstar->w[3] = Cstar.w[3];
  ptr_Cstar->w[2] = Cstar.w[2];
  ptr_Cstar->w[1] = Cstar.w[1];
  ptr_Cstar->w[0] = Cstar.w[0];

}