forked from OSchip/llvm-project
77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
/* This file is distributed under the University of Illinois Open Source
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* License. See LICENSE.TXT for details.
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*/
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/* long double __gcc_qsub(long double x, long double y);
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* This file implements the PowerPC 128-bit double-double add operation.
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* This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)
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*/
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#include "DD.h"
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long double __gcc_qsub(long double x, long double y)
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{
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static const uint32_t infinityHi = UINT32_C(0x7ff00000);
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DD dst = { .ld = x }, src = { .ld = y };
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register double A = dst.s.hi, a = dst.s.lo,
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B = -src.s.hi, b = -src.s.lo;
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/* If both operands are zero: */
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if ((A == 0.0) && (B == 0.0)) {
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dst.s.hi = A + B;
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dst.s.lo = 0.0;
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return dst.ld;
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}
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/* If either operand is NaN or infinity: */
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const doublebits abits = { .d = A };
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const doublebits bbits = { .d = B };
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if ((((uint32_t)(abits.x >> 32) & infinityHi) == infinityHi) ||
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(((uint32_t)(bbits.x >> 32) & infinityHi) == infinityHi)) {
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dst.s.hi = A + B;
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dst.s.lo = 0.0;
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return dst.ld;
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}
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/* If the computation overflows: */
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/* This may be playing things a little bit fast and loose, but it will do for a start. */
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const double testForOverflow = A + (B + (a + b));
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const doublebits testbits = { .d = testForOverflow };
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if (((uint32_t)(testbits.x >> 32) & infinityHi) == infinityHi) {
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dst.s.hi = testForOverflow;
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dst.s.lo = 0.0;
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return dst.ld;
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}
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double H, h;
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double T, t;
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double W, w;
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double Y;
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H = B + (A - (A + B));
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T = b + (a - (a + b));
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h = A + (B - (A + B));
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t = a + (b - (a + b));
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if (local_fabs(A) <= local_fabs(B))
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w = (a + b) + h;
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else
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w = (a + b) + H;
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W = (A + B) + w;
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Y = (A + B) - W;
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Y += w;
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if (local_fabs(a) <= local_fabs(b))
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w = t + Y;
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else
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w = T + Y;
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dst.s.hi = Y = W + w;
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dst.s.lo = (W - Y) + w;
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return dst.ld;
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}
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