mulsf3.c revision 296373
1//===-- lib/mulsf3.c - Single-precision multiplication ------------*- C -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is dual licensed under the MIT and the University of Illinois Open 6// Source Licenses. 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 18ARM_EABI_FNALIAS(fmul, mulsf3) 19 20COMPILER_RT_ABI fp_t 21__mulsf3(fp_t a, fp_t b) { 22 23 const unsigned int aExponent = toRep(a) >> significandBits & maxExponent; 24 const unsigned int bExponent = toRep(b) >> significandBits & maxExponent; 25 const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit; 26 27 rep_t aSignificand = toRep(a) & significandMask; 28 rep_t bSignificand = toRep(b) & significandMask; 29 int scale = 0; 30 31 // Detect if a or b is zero, denormal, infinity, or NaN. 32 if (aExponent-1U >= maxExponent-1U || bExponent-1U >= maxExponent-1U) { 33 34 const rep_t aAbs = toRep(a) & absMask; 35 const rep_t bAbs = toRep(b) & absMask; 36 37 // NaN * anything = qNaN 38 if (aAbs > infRep) return fromRep(toRep(a) | quietBit); 39 // anything * NaN = qNaN 40 if (bAbs > infRep) return fromRep(toRep(b) | quietBit); 41 42 if (aAbs == infRep) { 43 // infinity * non-zero = +/- infinity 44 if (bAbs) return fromRep(aAbs | productSign); 45 // infinity * zero = NaN 46 else return fromRep(qnanRep); 47 } 48 49 if (bAbs == infRep) { 50 // non-zero * infinity = +/- infinity 51 if (aAbs) return fromRep(bAbs | productSign); 52 // zero * infinity = NaN 53 else return fromRep(qnanRep); 54 } 55 56 // zero * anything = +/- zero 57 if (!aAbs) return fromRep(productSign); 58 // anything * zero = +/- zero 59 if (!bAbs) return fromRep(productSign); 60 61 // one or both of a or b is denormal, the other (if applicable) is a 62 // normal number. Renormalize one or both of a and b, and set scale to 63 // include the necessary exponent adjustment. 64 if (aAbs < implicitBit) scale += normalize(&aSignificand); 65 if (bAbs < implicitBit) scale += normalize(&bSignificand); 66 } 67 68 // Or in the implicit significand bit. (If we fell through from the 69 // denormal path it was already set by normalize( ), but setting it twice 70 // won't hurt anything.) 71 aSignificand |= implicitBit; 72 bSignificand |= implicitBit; 73 74 // Get the significand of a*b. Before multiplying the significands, shift 75 // one of them left to left-align it in the field. Thus, the product will 76 // have (exponentBits + 2) integral digits, all but two of which must be 77 // zero. Normalizing this result is just a conditional left-shift by one 78 // and bumping the exponent accordingly. 79 rep_t productHi, productLo; 80 wideMultiply(aSignificand, bSignificand << exponentBits, 81 &productHi, &productLo); 82 83 int productExponent = aExponent + bExponent - exponentBias + scale; 84 85 // Normalize the significand, adjust exponent if needed. 86 if (productHi & implicitBit) productExponent++; 87 else wideLeftShift(&productHi, &productLo, 1); 88 89 // If we have overflowed the type, return +/- infinity. 90 if (productExponent >= maxExponent) return fromRep(infRep | productSign); 91 92 if (productExponent <= 0) { 93 // Result is denormal before rounding, the exponent is zero and we 94 // need to shift the significand. 95 wideRightShiftWithSticky(&productHi, &productLo, 1U - (unsigned)productExponent); 96 } 97 98 else { 99 // Result is normal before rounding; insert the exponent. 100 productHi &= significandMask; 101 productHi |= (rep_t)productExponent << significandBits; 102 } 103 104 // Insert the sign of the result: 105 productHi |= productSign; 106 107 // Final rounding. The final result may overflow to infinity, or underflow 108 // to zero, but those are the correct results in those cases. 109 if (productLo > signBit) productHi++; 110 if (productLo == signBit) productHi += productHi & 1; 111 return fromRep(productHi); 112} 113