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1// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.2// See https://llvm.org/LICENSE.txt for license information.3// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception4 5// long double __gcc_qsub(long double x, long double y);6// This file implements the PowerPC 128-bit double-double add operation.7// This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)8 9#include "DD.h"10 11long double __gcc_qsub(long double x, long double y) {12 static const uint32_t infinityHi = UINT32_C(0x7ff00000);13 14 DD dst = {.ld = x}, src = {.ld = y};15 16 register double A = dst.s.hi, a = dst.s.lo, B = -src.s.hi, b = -src.s.lo;17 18 // If both operands are zero:19 if ((A == 0.0) && (B == 0.0)) {20 dst.s.hi = A + B;21 dst.s.lo = 0.0;22 return dst.ld;23 }24 25 // If either operand is NaN or infinity:26 const doublebits abits = {.d = A};27 const doublebits bbits = {.d = B};28 if ((((uint32_t)(abits.x >> 32) & infinityHi) == infinityHi) ||29 (((uint32_t)(bbits.x >> 32) & infinityHi) == infinityHi)) {30 dst.s.hi = A + B;31 dst.s.lo = 0.0;32 return dst.ld;33 }34 35 // If the computation overflows:36 // This may be playing things a little bit fast and loose, but it will do for37 // a start.38 const double testForOverflow = A + (B + (a + b));39 const doublebits testbits = {.d = testForOverflow};40 if (((uint32_t)(testbits.x >> 32) & infinityHi) == infinityHi) {41 dst.s.hi = testForOverflow;42 dst.s.lo = 0.0;43 return dst.ld;44 }45 46 double H, h;47 double T, t;48 double W, w;49 double Y;50 51 H = B + (A - (A + B));52 T = b + (a - (a + b));53 h = A + (B - (A + B));54 t = a + (b - (a + b));55 56 if (local_fabs(A) <= local_fabs(B))57 w = (a + b) + h;58 else59 w = (a + b) + H;60 61 W = (A + B) + w;62 Y = (A + B) - W;63 Y += w;64 65 if (local_fabs(a) <= local_fabs(b))66 w = t + Y;67 else68 w = T + Y;69 70 dst.s.hi = Y = W + w;71 dst.s.lo = (W - Y) + w;72 73 return dst.ld;74}75