3e5bb7eece
PR libgcc/66883
* config/epiphany/udivsi3-float.c: Fix CONCISE test, and comment typo.
N.B., this is not active code, just documenting a previous approach for this
function in C.
From-SVN: r229236
126 lines
2.9 KiB
C
126 lines
2.9 KiB
C
/* Generic unsigned 32 bit division implementation.
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Copyright (C) 2009-2015 Free Software Foundation, Inc.
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Contributed by Embecosm on behalf of Adapteva, Inc.
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This file is part of GCC.
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This file is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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This file is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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typedef union { unsigned int i; float f; } fu;
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unsigned int __udivsi3 (unsigned int a, unsigned int b);
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unsigned int
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__udivsi3 (unsigned int a, unsigned int b)
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{
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unsigned int d, t, s0, s1, s2, r0, r1;
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fu u0, u1, u2, u1b, u2b;
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if (b > a)
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return 0;
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if ((int) b < 0)
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return 1;
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/* Assuming B is nonzero, compute S0 such that 0 <= S0,
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(B << S0+1) does not overflow,
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A < 4.01 * (B << S0), with S0 chosen as small as possible
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without taking to much time calculating. */
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#ifdef CONVERT_UNSIGNED
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u0.f = a;
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u1.f = b;
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#else /* !CONVERT_UNSIGNED */
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u0.f = (int) a;
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u1.f = (int) b;
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#ifdef CONCISE
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if ((int) a < 0)
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u0.i = (a >> 8) - 0x00800000 + 0x3f800000 + (31 << 23);
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#else /* To use flag setting / cmove, this can be written as: */
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{
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unsigned c = 0xff800000 - 0x4f000000;
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t = (int)a >> 8;
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if (t >= c)
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u0.i = (t - c);
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}
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#endif
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#endif /* !CONVERT_UNSIGNED */
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s0 = u0.i + 1 /* Compensate for rounding errors. */
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- 0x00800000 /* adjust by one */ ;
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s0 = s0 - u1.i;
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s0 = (int)s0 >= 0 ? s0 : 0;
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s0 >>= 23;
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b <<= s0;
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r1 = 0;
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r0 = 1 << s0;
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a = ((t=a) - b);
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if (a <= t)
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{
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r1 += r0;
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a = ((t=a) - b);
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if (a <= t)
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do {
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r1 += r0;
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a = ((t=a) - b);
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} while (a <= t);
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}
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a += b;
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d = b - 1;
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#define STEP(n) case n: a += a; t = a - d; if (t <= a) a = t;
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switch (s0)
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{
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STEP (31)
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STEP (30)
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STEP (29)
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STEP (28)
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STEP (27)
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STEP (26)
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STEP (25)
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STEP (24)
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STEP (23)
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STEP (22)
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STEP (21)
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STEP (20)
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STEP (19)
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STEP (18)
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STEP (17)
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STEP (16)
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STEP (15)
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STEP (14)
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STEP (13)
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STEP (12)
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STEP (11)
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STEP (10)
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STEP (9)
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STEP (8)
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STEP (7)
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STEP (6)
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STEP (5)
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STEP (4)
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STEP (3)
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STEP (2)
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STEP (1)
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case 0: ;
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}
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r0 = r1 | (r0-1 & a);
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return r0;
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}
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