// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // long double __gcc_qsub(long double x, long double y); // This file implements the PowerPC 128-bit double-double add operation. // This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!) #include "DD.h" long double __gcc_qsub(long double x, long double y) { static const uint32_t infinityHi = UINT32_C(0x7ff00000); DD dst = {.ld = x}, src = {.ld = y}; register double A = dst.s.hi, a = dst.s.lo, B = -src.s.hi, b = -src.s.lo; // If both operands are zero: if ((A == 0.0) && (B == 0.0)) { dst.s.hi = A + B; dst.s.lo = 0.0; return dst.ld; } // If either operand is NaN or infinity: const doublebits abits = {.d = A}; const doublebits bbits = {.d = B}; if ((((uint32_t)(abits.x >> 32) & infinityHi) == infinityHi) || (((uint32_t)(bbits.x >> 32) & infinityHi) == infinityHi)) { dst.s.hi = A + B; dst.s.lo = 0.0; return dst.ld; } // If the computation overflows: // This may be playing things a little bit fast and loose, but it will do for // a start. const double testForOverflow = A + (B + (a + b)); const doublebits testbits = {.d = testForOverflow}; if (((uint32_t)(testbits.x >> 32) & infinityHi) == infinityHi) { dst.s.hi = testForOverflow; dst.s.lo = 0.0; return dst.ld; } double H, h; double T, t; double W, w; double Y; H = B + (A - (A + B)); T = b + (a - (a + b)); h = A + (B - (A + B)); t = a + (b - (a + b)); if (local_fabs(A) <= local_fabs(B)) w = (a + b) + h; else w = (a + b) + H; W = (A + B) + w; Y = (A + B) - W; Y += w; if (local_fabs(a) <= local_fabs(b)) w = t + Y; else w = T + Y; dst.s.hi = Y = W + w; dst.s.lo = (W - Y) + w; return dst.ld; } |