diff options
| -rw-r--r-- | fpu/softfloat.c | 35 | ||||
| -rw-r--r-- | include/fpu/softfloat-macros.h | 34 |
2 files changed, 52 insertions, 17 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 71da0f6..46ae206 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; diff --git a/include/fpu/softfloat-macros.h b/include/fpu/softfloat-macros.h index edc6821..a1d99c7 100644 --- a/include/fpu/softfloat-macros.h +++ b/include/fpu/softfloat-macros.h @@ -329,15 +329,30 @@ static inline void | pieces which are stored at the locations pointed to by `z0Ptr' and `z1Ptr'. *----------------------------------------------------------------------------*/ -static inline void - shortShift128Left( - uint64_t a0, uint64_t a1, int count, uint64_t *z0Ptr, uint64_t *z1Ptr) +static inline void shortShift128Left(uint64_t a0, uint64_t a1, int count, + uint64_t *z0Ptr, uint64_t *z1Ptr) { + *z1Ptr = a1 << count; + *z0Ptr = count == 0 ? a0 : (a0 << count) | (a1 >> (-count & 63)); +} - *z1Ptr = a1<<count; - *z0Ptr = - ( count == 0 ) ? a0 : ( a0<<count ) | ( a1>>( ( - count ) & 63 ) ); +/*---------------------------------------------------------------------------- +| Shifts the 128-bit value formed by concatenating `a0' and `a1' left by the +| number of bits given in `count'. Any bits shifted off are lost. The value +| of `count' may be greater than 64. The result is broken into two 64-bit +| pieces which are stored at the locations pointed to by `z0Ptr' and `z1Ptr'. +*----------------------------------------------------------------------------*/ +static inline void shift128Left(uint64_t a0, uint64_t a1, int count, + uint64_t *z0Ptr, uint64_t *z1Ptr) +{ + if (count < 64) { + *z1Ptr = a1 << count; + *z0Ptr = count == 0 ? a0 : (a0 << count) | (a1 >> (-count & 63)); + } else { + *z1Ptr = 0; + *z0Ptr = a1 << (count - 64); + } } /*---------------------------------------------------------------------------- @@ -619,7 +634,8 @@ static inline uint64_t estimateDiv128To64(uint64_t a0, uint64_t a1, uint64_t b) * * Licensed under the GPLv2/LGPLv3 */ -static inline uint64_t div128To64(uint64_t n0, uint64_t n1, uint64_t d) +static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1, + uint64_t n0, uint64_t d) { uint64_t d0, d1, q0, q1, r1, r0, m; @@ -658,8 +674,8 @@ static inline uint64_t div128To64(uint64_t n0, uint64_t n1, uint64_t d) } r0 -= m; - /* Return remainder in LSB */ - return (q1 << 32) | q0 | (r0 != 0); + *r = r0; + return (q1 << 32) | q0; } /*---------------------------------------------------------------------------- |