forked from OSchip/llvm-project
129 lines
4.4 KiB
C
129 lines
4.4 KiB
C
//===---- lib/fp_mul_impl.inc - floating point multiplication -----*- C -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements soft-float multiplication with the IEEE-754 default
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// rounding (to nearest, ties to even).
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//
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//===----------------------------------------------------------------------===//
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#include "fp_lib.h"
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static __inline fp_t __mulXf3__(fp_t a, fp_t b) {
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const unsigned int aExponent = toRep(a) >> significandBits & maxExponent;
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const unsigned int bExponent = toRep(b) >> significandBits & maxExponent;
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const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit;
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rep_t aSignificand = toRep(a) & significandMask;
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rep_t bSignificand = toRep(b) & significandMask;
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int scale = 0;
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// Detect if a or b is zero, denormal, infinity, or NaN.
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if (aExponent - 1U >= maxExponent - 1U ||
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bExponent - 1U >= maxExponent - 1U) {
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const rep_t aAbs = toRep(a) & absMask;
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const rep_t bAbs = toRep(b) & absMask;
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// NaN * anything = qNaN
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if (aAbs > infRep)
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return fromRep(toRep(a) | quietBit);
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// anything * NaN = qNaN
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if (bAbs > infRep)
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return fromRep(toRep(b) | quietBit);
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if (aAbs == infRep) {
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// infinity * non-zero = +/- infinity
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if (bAbs)
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return fromRep(aAbs | productSign);
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// infinity * zero = NaN
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else
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return fromRep(qnanRep);
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}
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if (bAbs == infRep) {
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// non-zero * infinity = +/- infinity
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if (aAbs)
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return fromRep(bAbs | productSign);
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// zero * infinity = NaN
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else
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return fromRep(qnanRep);
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}
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// zero * anything = +/- zero
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if (!aAbs)
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return fromRep(productSign);
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// anything * zero = +/- zero
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if (!bAbs)
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return fromRep(productSign);
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// One or both of a or b is denormal. The other (if applicable) is a
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// normal number. Renormalize one or both of a and b, and set scale to
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// include the necessary exponent adjustment.
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if (aAbs < implicitBit)
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scale += normalize(&aSignificand);
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if (bAbs < implicitBit)
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scale += normalize(&bSignificand);
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}
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// Set the implicit significand bit. If we fell through from the
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// denormal path it was already set by normalize( ), but setting it twice
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// won't hurt anything.
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aSignificand |= implicitBit;
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bSignificand |= implicitBit;
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// Perform a basic multiplication on the significands. One of them must be
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// shifted beforehand to be aligned with the exponent.
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rep_t productHi, productLo;
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wideMultiply(aSignificand, bSignificand << exponentBits, &productHi,
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&productLo);
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int productExponent = aExponent + bExponent - exponentBias + scale;
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// Normalize the significand and adjust the exponent if needed.
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if (productHi & implicitBit)
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productExponent++;
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else
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wideLeftShift(&productHi, &productLo, 1);
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// If we have overflowed the type, return +/- infinity.
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if (productExponent >= maxExponent)
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return fromRep(infRep | productSign);
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if (productExponent <= 0) {
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// The result is denormal before rounding.
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//
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// If the result is so small that it just underflows to zero, return
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// zero with the appropriate sign. Mathematically, there is no need to
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// handle this case separately, but we make it a special case to
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// simplify the shift logic.
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const unsigned int shift = REP_C(1) - (unsigned int)productExponent;
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if (shift >= typeWidth)
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return fromRep(productSign);
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// Otherwise, shift the significand of the result so that the round
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// bit is the high bit of productLo.
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wideRightShiftWithSticky(&productHi, &productLo, shift);
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} else {
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// The result is normal before rounding. Insert the exponent.
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productHi &= significandMask;
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productHi |= (rep_t)productExponent << significandBits;
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}
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// Insert the sign of the result.
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productHi |= productSign;
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// Perform the final rounding. The final result may overflow to infinity,
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// or underflow to zero, but those are the correct results in those cases.
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// We use the default IEEE-754 round-to-nearest, ties-to-even rounding mode.
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if (productLo > signBit)
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productHi++;
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if (productLo == signBit)
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productHi += productHi & 1;
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return fromRep(productHi);
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}
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