mulsf3.c revision 222656 
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#include "abi.h"
15
16#define SINGLE_PRECISION
17#include "fp_lib.h"
18
19ARM_EABI_FNALIAS(fmul, mulsf3);
20
21COMPILER_RT_ABI fp_t
22__mulsf3(fp_t a, fp_t b) {
23
24    const unsigned int aExponent = toRep(a) >> significandBits & maxExponent;
25    const unsigned int bExponent = toRep(b) >> significandBits & maxExponent;
26    const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit;
27
28    rep_t aSignificand = toRep(a) & significandMask;
29    rep_t bSignificand = toRep(b) & significandMask;
30    int scale = 0;
31
32    // Detect if a or b is zero, denormal, infinity, or NaN.
33    if (aExponent-1U >= maxExponent-1U || bExponent-1U >= maxExponent-1U) {
34
35        const rep_t aAbs = toRep(a) & absMask;
36        const rep_t bAbs = toRep(b) & absMask;
37
38        // NaN * anything = qNaN
39        if (aAbs > infRep) return fromRep(toRep(a) | quietBit);
40        // anything * NaN = qNaN
41        if (bAbs > infRep) return fromRep(toRep(b) | quietBit);
42
43        if (aAbs == infRep) {
44            // infinity * non-zero = +/- infinity
45            if (bAbs) return fromRep(aAbs | productSign);
46            // infinity * zero = NaN
47            else return fromRep(qnanRep);
48        }
49
50        if (bAbs == infRep) {
51            // non-zero * infinity = +/- infinity
52            if (aAbs) return fromRep(bAbs | productSign);
53            // zero * infinity = NaN
54            else return fromRep(qnanRep);
55        }
56
57        // zero * anything = +/- zero
58        if (!aAbs) return fromRep(productSign);
59        // anything * zero = +/- zero
60        if (!bAbs) return fromRep(productSign);
61
62        // one or both of a or b is denormal, the other (if applicable) is a
63        // normal number.  Renormalize one or both of a and b, and set scale to
64        // include the necessary exponent adjustment.
65        if (aAbs < implicitBit) scale += normalize(&aSignificand);
66        if (bAbs < implicitBit) scale += normalize(&bSignificand);
67    }
68
69    // Or in the implicit significand bit.  (If we fell through from the
70    // denormal path it was already set by normalize( ), but setting it twice
71    // won't hurt anything.)
72    aSignificand |= implicitBit;
73    bSignificand |= implicitBit;
74
75    // Get the significand of a*b.  Before multiplying the significands, shift
76    // one of them left to left-align it in the field.  Thus, the product will
77    // have (exponentBits + 2) integral digits, all but two of which must be
78    // zero.  Normalizing this result is just a conditional left-shift by one
79    // and bumping the exponent accordingly.
80    rep_t productHi, productLo;
81    wideMultiply(aSignificand, bSignificand << exponentBits,
82                 &productHi, &productLo);
83
84    int productExponent = aExponent + bExponent - exponentBias + scale;
85
86    // Normalize the significand, adjust exponent if needed.
87    if (productHi & implicitBit) productExponent++;
88    else wideLeftShift(&productHi, &productLo, 1);
89
90    // If we have overflowed the type, return +/- infinity.
91    if (productExponent >= maxExponent) return fromRep(infRep | productSign);
92
93    if (productExponent <= 0) {
94        // Result is denormal before rounding, the exponent is zero and we
95        // need to shift the significand.
96        wideRightShiftWithSticky(&productHi, &productLo, 1 - productExponent);
97    }
98
99    else {
100        // Result is normal before rounding; insert the exponent.
101        productHi &= significandMask;
102        productHi |= (rep_t)productExponent << significandBits;
103    }
104
105    // Insert the sign of the result:
106    productHi |= productSign;
107
108    // Final rounding.  The final result may overflow to infinity, or underflow
109    // to zero, but those are the correct results in those cases.
110    if (productLo > signBit) productHi++;
111    if (productLo == signBit) productHi += productHi & 1;
112    return fromRep(productHi);
113}
114