diff options
Diffstat (limited to 'fpu/softfloat.c')
| -rw-r--r-- | fpu/softfloat.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 71da0f68bb..46ae206172 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -1112,19 +1112,38 @@ static FloatParts div_floats(FloatParts a, FloatParts b, float_status *s) bool sign = a.sign ^ b.sign; if (a.cls == float_class_normal && b.cls == float_class_normal) { - uint64_t temp_lo, temp_hi; + uint64_t n0, n1, q, r; int exp = a.exp - b.exp; + + /* + * We want a 2*N / N-bit division to produce exactly an N-bit + * result, so that we do not lose any precision and so that we + * do not have to renormalize afterward. If A.frac < B.frac, + * then division would produce an (N-1)-bit result; shift A left + * by one to produce the an N-bit result, and decrement the + * exponent to match. + * + * The udiv_qrnnd algorithm that we're using requires normalization, + * i.e. the msb of the denominator must be set. Since we know that + * DECOMPOSED_BINARY_POINT is msb-1, the inputs must be shifted left + * by one (more), and the remainder must be shifted right by one. + */ if (a.frac < b.frac) { exp -= 1; - shortShift128Left(0, a.frac, DECOMPOSED_BINARY_POINT + 1, - &temp_hi, &temp_lo); + shift128Left(0, a.frac, DECOMPOSED_BINARY_POINT + 2, &n1, &n0); } else { - shortShift128Left(0, a.frac, DECOMPOSED_BINARY_POINT, - &temp_hi, &temp_lo); + shift128Left(0, a.frac, DECOMPOSED_BINARY_POINT + 1, &n1, &n0); } - /* LSB of quot is set if inexact which roundandpack will use - * to set flags. Yet again we re-use a for the result */ - a.frac = div128To64(temp_lo, temp_hi, b.frac); + q = udiv_qrnnd(&r, n1, n0, b.frac << 1); + + /* + * Set lsb if there is a remainder, to set inexact. + * As mentioned above, to find the actual value of the remainder we + * would need to shift right, but (1) we are only concerned about + * non-zero-ness, and (2) the remainder will always be even because + * both inputs to the division primitive are even. + */ + a.frac = q | (r != 0); a.sign = sign; a.exp = exp; return a; |