404 lines
12 KiB
C
404 lines
12 KiB
C
/* IEEE floating point support routines, for GDB, the GNU Debugger.
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Copyright (C) 1991, 1994, 1999 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
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#include "floatformat.h"
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#include <math.h> /* ldexp */
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#ifdef __STDC__
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#include <stddef.h>
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extern void *memcpy (void *s1, const void *s2, size_t n);
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extern void *memset (void *s, int c, size_t n);
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#else
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extern char *memcpy ();
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extern char *memset ();
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#endif
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/* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
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going to bother with trying to muck around with whether it is defined in
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a system header, what we do if not, etc. */
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#define FLOATFORMAT_CHAR_BIT 8
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/* floatformats for IEEE single and double, big and little endian. */
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const struct floatformat floatformat_ieee_single_big =
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{
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floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23, floatformat_intbit_no
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};
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const struct floatformat floatformat_ieee_single_little =
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{
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floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23, floatformat_intbit_no
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};
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const struct floatformat floatformat_ieee_double_big =
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{
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floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52, floatformat_intbit_no
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};
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const struct floatformat floatformat_ieee_double_little =
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{
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floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52, floatformat_intbit_no
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};
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/* floatformat for IEEE double, little endian byte order, with big endian word
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ordering, as on the ARM. */
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const struct floatformat floatformat_ieee_double_littlebyte_bigword =
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{
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floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52, floatformat_intbit_no
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};
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const struct floatformat floatformat_i387_ext =
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{
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floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
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floatformat_intbit_yes
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};
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const struct floatformat floatformat_m68881_ext =
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{
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/* Note that the bits from 16 to 31 are unused. */
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floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64, floatformat_intbit_yes
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};
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const struct floatformat floatformat_i960_ext =
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{
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/* Note that the bits from 0 to 15 are unused. */
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floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
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floatformat_intbit_yes
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};
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const struct floatformat floatformat_m88110_ext =
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{
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#ifdef HARRIS_FLOAT_FORMAT
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/* Harris uses raw format 128 bytes long, but the number is just an ieee
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double, and the last 64 bits are wasted. */
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floatformat_big,128, 0, 1, 11, 0x3ff, 0x7ff, 12, 52,
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floatformat_intbit_no
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#else
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floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
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floatformat_intbit_yes
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#endif /* HARRIS_FLOAT_FORMAT */
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};
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const struct floatformat floatformat_arm_ext =
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{
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/* Bits 1 to 16 are unused. */
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floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
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floatformat_intbit_yes
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};
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static unsigned long get_field PARAMS ((unsigned char *,
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enum floatformat_byteorders,
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unsigned int,
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unsigned int,
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unsigned int));
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/* Extract a field which starts at START and is LEN bytes long. DATA and
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TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER. */
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static unsigned long
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get_field (data, order, total_len, start, len)
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unsigned char *data;
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enum floatformat_byteorders order;
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unsigned int total_len;
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unsigned int start;
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unsigned int len;
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{
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unsigned long result;
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unsigned int cur_byte;
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int cur_bitshift;
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/* Start at the least significant part of the field. */
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cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
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cur_bitshift =
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((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
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result = *(data + cur_byte) >> (-cur_bitshift);
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cur_bitshift += FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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++cur_byte;
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else
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--cur_byte;
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/* Move towards the most significant part of the field. */
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while ((unsigned int) cur_bitshift < len)
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{
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if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
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/* This is the last byte; zero out the bits which are not part of
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this field. */
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result |=
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(*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
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<< cur_bitshift;
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else
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result |= *(data + cur_byte) << cur_bitshift;
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cur_bitshift += FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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++cur_byte;
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else
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--cur_byte;
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}
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return result;
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}
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#ifndef min
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#define min(a, b) ((a) < (b) ? (a) : (b))
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#endif
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/* Convert from FMT to a double.
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FROM is the address of the extended float.
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Store the double in *TO. */
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void
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floatformat_to_double (fmt, from, to)
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const struct floatformat *fmt;
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char *from;
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double *to;
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{
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unsigned char *ufrom = (unsigned char *)from;
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double dto;
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long exponent;
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unsigned long mant;
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unsigned int mant_bits, mant_off;
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int mant_bits_left;
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int special_exponent; /* It's a NaN, denorm or zero */
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exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
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fmt->exp_start, fmt->exp_len);
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/* Note that if exponent indicates a NaN, we can't really do anything useful
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(not knowing if the host has NaN's, or how to build one). So it will
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end up as an infinity or something close; that is OK. */
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mant_bits_left = fmt->man_len;
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mant_off = fmt->man_start;
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dto = 0.0;
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special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
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/* Don't bias zero's, denorms or NaNs. */
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if (!special_exponent)
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exponent -= fmt->exp_bias;
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/* Build the result algebraically. Might go infinite, underflow, etc;
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who cares. */
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/* If this format uses a hidden bit, explicitly add it in now. Otherwise,
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increment the exponent by one to account for the integer bit. */
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if (!special_exponent)
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{
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if (fmt->intbit == floatformat_intbit_no)
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dto = ldexp (1.0, exponent);
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else
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exponent++;
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}
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while (mant_bits_left > 0)
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{
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mant_bits = min (mant_bits_left, 32);
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mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
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mant_off, mant_bits);
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dto += ldexp ((double)mant, exponent - mant_bits);
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exponent -= mant_bits;
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mant_off += mant_bits;
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mant_bits_left -= mant_bits;
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}
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/* Negate it if negative. */
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if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
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dto = -dto;
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*to = dto;
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}
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static void put_field PARAMS ((unsigned char *, enum floatformat_byteorders,
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unsigned int,
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unsigned int,
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unsigned int,
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unsigned long));
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/* Set a field which starts at START and is LEN bytes long. DATA and
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TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER. */
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static void
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put_field (data, order, total_len, start, len, stuff_to_put)
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unsigned char *data;
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enum floatformat_byteorders order;
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unsigned int total_len;
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unsigned int start;
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unsigned int len;
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unsigned long stuff_to_put;
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{
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unsigned int cur_byte;
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int cur_bitshift;
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/* Start at the least significant part of the field. */
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cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
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cur_bitshift =
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((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
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*(data + cur_byte) &=
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~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
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*(data + cur_byte) |=
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(stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
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cur_bitshift += FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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++cur_byte;
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else
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--cur_byte;
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/* Move towards the most significant part of the field. */
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while ((unsigned int) cur_bitshift < len)
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{
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if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
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{
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/* This is the last byte. */
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*(data + cur_byte) &=
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~((1 << (len - cur_bitshift)) - 1);
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*(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
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}
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else
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*(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
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& ((1 << FLOATFORMAT_CHAR_BIT) - 1));
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cur_bitshift += FLOATFORMAT_CHAR_BIT;
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if (order == floatformat_little)
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++cur_byte;
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else
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--cur_byte;
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}
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}
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/* The converse: convert the double *FROM to an extended float
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and store where TO points. Neither FROM nor TO have any alignment
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restrictions. */
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void
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floatformat_from_double (fmt, from, to)
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const struct floatformat *fmt;
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double *from;
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char *to;
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{
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double dfrom;
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int exponent;
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double mant;
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unsigned int mant_bits, mant_off;
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int mant_bits_left;
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unsigned char *uto = (unsigned char *)to;
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memcpy (&dfrom, from, sizeof (dfrom));
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memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
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if (dfrom == 0)
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return; /* Result is zero */
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if (dfrom != dfrom)
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{
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/* From is NaN */
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put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
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fmt->exp_len, fmt->exp_nan);
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/* Be sure it's not infinity, but NaN value is irrel */
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put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
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32, 1);
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return;
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}
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/* If negative, set the sign bit. */
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if (dfrom < 0)
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{
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put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
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dfrom = -dfrom;
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}
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/* How to tell an infinity from an ordinary number? FIXME-someday */
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mant = frexp (dfrom, &exponent);
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put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start, fmt->exp_len,
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exponent + fmt->exp_bias - 1);
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mant_bits_left = fmt->man_len;
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mant_off = fmt->man_start;
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while (mant_bits_left > 0)
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{
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unsigned long mant_long;
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mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
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mant *= 4294967296.0;
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mant_long = (unsigned long)mant;
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mant -= mant_long;
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/* If the integer bit is implicit, then we need to discard it.
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If we are discarding a zero, we should be (but are not) creating
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a denormalized number which means adjusting the exponent
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(I think). */
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if ((unsigned int) mant_bits_left == fmt->man_len
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&& fmt->intbit == floatformat_intbit_no)
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{
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mant_long &= 0x7fffffff;
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mant_bits -= 1;
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}
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else if (mant_bits < 32)
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{
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/* The bits we want are in the most significant MANT_BITS bits of
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mant_long. Move them to the least significant. */
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mant_long >>= 32 - mant_bits;
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}
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put_field (uto, fmt->byteorder, fmt->totalsize,
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mant_off, mant_bits, mant_long);
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mant_off += mant_bits;
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mant_bits_left -= mant_bits;
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}
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}
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#ifdef IEEE_DEBUG
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/* This is to be run on a host which uses IEEE floating point. */
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void
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ieee_test (n)
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double n;
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{
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double result;
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char exten[16];
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floatformat_to_double (&floatformat_ieee_double_big, &n, &result);
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if (n != result)
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printf ("Differ(to): %.20g -> %.20g\n", n, result);
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floatformat_from_double (&floatformat_ieee_double_big, &n, &result);
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if (n != result)
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printf ("Differ(from): %.20g -> %.20g\n", n, result);
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floatformat_from_double (&floatformat_m68881_ext, &n, exten);
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floatformat_to_double (&floatformat_m68881_ext, exten, &result);
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if (n != result)
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printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
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#if IEEE_DEBUG > 1
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/* This is to be run on a host which uses 68881 format. */
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{
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long double ex = *(long double *)exten;
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if (ex != n)
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printf ("Differ(from vs. extended): %.20g\n", n);
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}
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#endif
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}
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int
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main ()
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{
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ieee_test (0.5);
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ieee_test (256.0);
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ieee_test (0.12345);
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ieee_test (234235.78907234);
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ieee_test (-512.0);
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ieee_test (-0.004321);
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return 0;
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}
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#endif
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