Stephen Canon | 5c6d2ec | 2010-07-01 17:58:24 +0000 | [diff] [blame^] | 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 | //===----------------------------------------------------------------------===// |
Stephen Canon | e508632 | 2010-07-01 15:52:42 +0000 | [diff] [blame] | 14 | |
| 15 | #define SINGLE_PRECISION |
| 16 | #include "fp_lib.h" |
| 17 | |
Stephen Canon | e508632 | 2010-07-01 15:52:42 +0000 | [diff] [blame] | 18 | // 32x32 --> 64 bit multiply |
| 19 | static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) { |
| 20 | const uint64_t product = (uint64_t)a*b; |
| 21 | *hi = product >> 32; |
| 22 | *lo = product; |
| 23 | } |
| 24 | |
| 25 | fp_t __mulsf3(fp_t a, fp_t b) { |
| 26 | |
| 27 | const unsigned int aExponent = toRep(a) >> significandBits & maxExponent; |
| 28 | const unsigned int bExponent = toRep(b) >> significandBits & maxExponent; |
| 29 | const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit; |
| 30 | |
| 31 | rep_t aSignificand = toRep(a) & significandMask; |
| 32 | rep_t bSignificand = toRep(b) & significandMask; |
| 33 | int scale = 0; |
| 34 | |
| 35 | // Detect if a or b is zero, denormal, infinity, or NaN. |
| 36 | if (aExponent-1U >= maxExponent-1U || bExponent-1U >= maxExponent-1U) { |
| 37 | |
| 38 | const rep_t aAbs = toRep(a) & absMask; |
| 39 | const rep_t bAbs = toRep(b) & absMask; |
| 40 | |
| 41 | // NaN * anything = qNaN |
| 42 | if (aAbs > infRep) return fromRep(toRep(a) | quietBit); |
| 43 | // anything * NaN = qNaN |
| 44 | if (bAbs > infRep) return fromRep(toRep(b) | quietBit); |
| 45 | |
| 46 | if (aAbs == infRep) { |
| 47 | // infinity * non-zero = +/- infinity |
| 48 | if (bAbs) return fromRep(aAbs | productSign); |
| 49 | // infinity * zero = NaN |
| 50 | else return fromRep(qnanRep); |
| 51 | } |
| 52 | |
| 53 | if (bAbs == infRep) { |
| 54 | // non-zero * infinity = +/- infinity |
| 55 | if (aAbs) return fromRep(bAbs | productSign); |
| 56 | // zero * infinity = NaN |
| 57 | else return fromRep(qnanRep); |
| 58 | } |
| 59 | |
| 60 | // zero * anything = +/- zero |
| 61 | if (!aAbs) return fromRep(productSign); |
| 62 | // anything * zero = +/- zero |
| 63 | if (!bAbs) return fromRep(productSign); |
| 64 | |
| 65 | // one or both of a or b is denormal, the other (if applicable) is a |
| 66 | // normal number. Renormalize one or both of a and b, and set scale to |
| 67 | // include the necessary exponent adjustment. |
| 68 | if (aAbs < implicitBit) scale += normalize(&aSignificand); |
| 69 | if (bAbs < implicitBit) scale += normalize(&bSignificand); |
| 70 | } |
| 71 | |
| 72 | // Or in the implicit significand bit. (If we fell through from the |
| 73 | // denormal path it was already set by normalize( ), but setting it twice |
| 74 | // won't hurt anything.) |
| 75 | aSignificand |= implicitBit; |
| 76 | bSignificand |= implicitBit; |
| 77 | |
| 78 | // Get the significand of a*b. Before multiplying the significands, shift |
| 79 | // one of them left to left-align it in the field. Thus, the product will |
| 80 | // have (exponentBits + 2) integral digits, all but two of which must be |
| 81 | // zero. Normalizing this result is just a conditional left-shift by one |
| 82 | // and bumping the exponent accordingly. |
| 83 | rep_t productHi, productLo; |
| 84 | wideMultiply(aSignificand, bSignificand << exponentBits, |
| 85 | &productHi, &productLo); |
| 86 | |
| 87 | int productExponent = aExponent + bExponent - exponentBias + scale; |
| 88 | |
| 89 | // Normalize the significand, adjust exponent if needed. |
| 90 | if (productHi & implicitBit) productExponent++; |
| 91 | else wideLeftShift(&productHi, &productLo, 1); |
| 92 | |
| 93 | // If we have overflowed the type, return +/- infinity. |
| 94 | if (productExponent >= maxExponent) return fromRep(infRep | productSign); |
| 95 | |
| 96 | if (productExponent <= 0) { |
| 97 | // Result is denormal before rounding, the exponent is zero and we |
| 98 | // need to shift the significand. |
| 99 | wideRightShiftWithSticky(&productHi, &productLo, 1 - productExponent); |
| 100 | } |
| 101 | |
| 102 | else { |
| 103 | // Result is normal before rounding; insert the exponent. |
| 104 | productHi &= significandMask; |
| 105 | productHi |= (rep_t)productExponent << significandBits; |
| 106 | } |
| 107 | |
| 108 | // Insert the sign of the result: |
| 109 | productHi |= productSign; |
| 110 | |
| 111 | // Final rounding. The final result may overflow to infinity, or underflow |
| 112 | // to zero, but those are the correct results in those cases. |
| 113 | if (productLo > signBit) productHi++; |
| 114 | if (productLo == signBit) productHi += productHi & 1; |
| 115 | return fromRep(productHi); |
| 116 | } |