mulsf3.c revision 215125
1//===-- lib/mulsf3.c - Single-precision multiplication ------------*- C -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements single-precision soft-float multiplication 11// with the IEEE-754 default rounding (to nearest, ties to even). 12// 13//===----------------------------------------------------------------------===// 14 15#define SINGLE_PRECISION 16#include "fp_lib.h" 17 18fp_t __mulsf3(fp_t a, fp_t b) { 19 20 const unsigned int aExponent = toRep(a) >> significandBits & maxExponent; 21 const unsigned int bExponent = toRep(b) >> significandBits & maxExponent; 22 const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit; 23 24 rep_t aSignificand = toRep(a) & significandMask; 25 rep_t bSignificand = toRep(b) & significandMask; 26 int scale = 0; 27 28 // Detect if a or b is zero, denormal, infinity, or NaN. 29 if (aExponent-1U >= maxExponent-1U || bExponent-1U >= maxExponent-1U) { 30 31 const rep_t aAbs = toRep(a) & absMask; 32 const rep_t bAbs = toRep(b) & absMask; 33 34 // NaN * anything = qNaN 35 if (aAbs > infRep) return fromRep(toRep(a) | quietBit); 36 // anything * NaN = qNaN 37 if (bAbs > infRep) return fromRep(toRep(b) | quietBit); 38 39 if (aAbs == infRep) { 40 // infinity * non-zero = +/- infinity 41 if (bAbs) return fromRep(aAbs | productSign); 42 // infinity * zero = NaN 43 else return fromRep(qnanRep); 44 } 45 46 if (bAbs == infRep) { 47 // non-zero * infinity = +/- infinity 48 if (aAbs) return fromRep(bAbs | productSign); 49 // zero * infinity = NaN 50 else return fromRep(qnanRep); 51 } 52 53 // zero * anything = +/- zero 54 if (!aAbs) return fromRep(productSign); 55 // anything * zero = +/- zero 56 if (!bAbs) return fromRep(productSign); 57 58 // one or both of a or b is denormal, the other (if applicable) is a 59 // normal number. Renormalize one or both of a and b, and set scale to 60 // include the necessary exponent adjustment. 61 if (aAbs < implicitBit) scale += normalize(&aSignificand); 62 if (bAbs < implicitBit) scale += normalize(&bSignificand); 63 } 64 65 // Or in the implicit significand bit. (If we fell through from the 66 // denormal path it was already set by normalize( ), but setting it twice 67 // won't hurt anything.) 68 aSignificand |= implicitBit; 69 bSignificand |= implicitBit; 70 71 // Get the significand of a*b. Before multiplying the significands, shift 72 // one of them left to left-align it in the field. Thus, the product will 73 // have (exponentBits + 2) integral digits, all but two of which must be 74 // zero. Normalizing this result is just a conditional left-shift by one 75 // and bumping the exponent accordingly. 76 rep_t productHi, productLo; 77 wideMultiply(aSignificand, bSignificand << exponentBits, 78 &productHi, &productLo); 79 80 int productExponent = aExponent + bExponent - exponentBias + scale; 81 82 // Normalize the significand, adjust exponent if needed. 83 if (productHi & implicitBit) productExponent++; 84 else wideLeftShift(&productHi, &productLo, 1); 85 86 // If we have overflowed the type, return +/- infinity. 87 if (productExponent >= maxExponent) return fromRep(infRep | productSign); 88 89 if (productExponent <= 0) { 90 // Result is denormal before rounding, the exponent is zero and we 91 // need to shift the significand. 92 wideRightShiftWithSticky(&productHi, &productLo, 1 - productExponent); 93 } 94 95 else { 96 // Result is normal before rounding; insert the exponent. 97 productHi &= significandMask; 98 productHi |= (rep_t)productExponent << significandBits; 99 } 100 101 // Insert the sign of the result: 102 productHi |= productSign; 103 104 // Final rounding. The final result may overflow to infinity, or underflow 105 // to zero, but those are the correct results in those cases. 106 if (productLo > signBit) productHi++; 107 if (productLo == signBit) productHi += productHi & 1; 108 return fromRep(productHi); 109} 110