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Diffstat (limited to 'lib/fp_lib.h')
| -rw-r--r-- | lib/fp_lib.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/lib/fp_lib.h b/lib/fp_lib.h new file mode 100644 index 000000000000..eac670d7f236 --- /dev/null +++ b/lib/fp_lib.h @@ -0,0 +1,143 @@ +//===-- lib/fp_lib.h - Floating-point utilities -------------------*- C -*-===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file is a configuration header for soft-float routines in compiler-rt. +// This file does not provide any part of the compiler-rt interface, but defines +// many useful constants and utility routines that are used in the +// implementation of the soft-float routines in compiler-rt. +// +// Assumes that float and double correspond to the IEEE-754 binary32 and +// binary64 types, respectively, and that integer endianness matches floating +// point endianness on the target platform. +// +//===----------------------------------------------------------------------===// + +#ifndef FP_LIB_HEADER +#define FP_LIB_HEADER + +#include <stdint.h> +#include <stdbool.h> +#include <limits.h> + +#if defined SINGLE_PRECISION + +typedef uint32_t rep_t; +typedef int32_t srep_t; +typedef float fp_t; +#define REP_C UINT32_C +#define significandBits 23 + +static inline int rep_clz(rep_t a) { + return __builtin_clz(a); +} + +// 32x32 --> 64 bit multiply +static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) { + const uint64_t product = (uint64_t)a*b; + *hi = product >> 32; + *lo = product; +} + +#elif defined DOUBLE_PRECISION + +typedef uint64_t rep_t; +typedef int64_t srep_t; +typedef double fp_t; +#define REP_C UINT64_C +#define significandBits 52 + +static inline int rep_clz(rep_t a) { +#if defined __LP64__ + return __builtin_clzl(a); +#else + if (a & REP_C(0xffffffff00000000)) + return __builtin_clz(a >> 32); + else + return 32 + __builtin_clz(a & REP_C(0xffffffff)); +#endif +} + +#define loWord(a) (a & 0xffffffffU) +#define hiWord(a) (a >> 32) + +// 64x64 -> 128 wide multiply for platforms that don't have such an operation; +// many 64-bit platforms have this operation, but they tend to have hardware +// floating-point, so we don't bother with a special case for them here. +static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) { + // Each of the component 32x32 -> 64 products + const uint64_t plolo = loWord(a) * loWord(b); + const uint64_t plohi = loWord(a) * hiWord(b); + const uint64_t philo = hiWord(a) * loWord(b); + const uint64_t phihi = hiWord(a) * hiWord(b); + // Sum terms that contribute to lo in a way that allows us to get the carry + const uint64_t r0 = loWord(plolo); + const uint64_t r1 = hiWord(plolo) + loWord(plohi) + loWord(philo); + *lo = r0 + (r1 << 32); + // Sum terms contributing to hi with the carry from lo + *hi = hiWord(plohi) + hiWord(philo) + hiWord(r1) + phihi; +} + +#else +#error Either SINGLE_PRECISION or DOUBLE_PRECISION must be defined. +#endif + +#define typeWidth (sizeof(rep_t)*CHAR_BIT) +#define exponentBits (typeWidth - significandBits - 1) +#define maxExponent ((1 << exponentBits) - 1) +#define exponentBias (maxExponent >> 1) + +#define implicitBit (REP_C(1) << significandBits) +#define significandMask (implicitBit - 1U) +#define signBit (REP_C(1) << (significandBits + exponentBits)) +#define absMask (signBit - 1U) +#define exponentMask (absMask ^ significandMask) +#define oneRep ((rep_t)exponentBias << significandBits) +#define infRep exponentMask +#define quietBit (implicitBit >> 1) +#define qnanRep (exponentMask | quietBit) + +static inline rep_t toRep(fp_t x) { + const union { fp_t f; rep_t i; } rep = {.f = x}; + return rep.i; +} + +static inline fp_t fromRep(rep_t x) { + const union { fp_t f; rep_t i; } rep = {.i = x}; + return rep.f; +} + +static inline int normalize(rep_t *significand) { + const int shift = rep_clz(*significand) - rep_clz(implicitBit); + *significand <<= shift; + return 1 - shift; +} + +static inline void wideLeftShift(rep_t *hi, rep_t *lo, int count) { + *hi = *hi << count | *lo >> (typeWidth - count); + *lo = *lo << count; +} + +static inline void wideRightShiftWithSticky(rep_t *hi, rep_t *lo, int count) { + if (count < typeWidth) { + const bool sticky = *lo << (typeWidth - count); + *lo = *hi << (typeWidth - count) | *lo >> count | sticky; + *hi = *hi >> count; + } + else if (count < 2*typeWidth) { + const bool sticky = *hi << (2*typeWidth - count) | *lo; + *lo = *hi >> (count - typeWidth) | sticky; + *hi = 0; + } else { + const bool sticky = *hi | *lo; + *lo = sticky; + *hi = 0; + } +} + +#endif // FP_LIB_HEADER |