lib/fp_lib.h

   1 //===-- lib/fp_lib.h - Floating-point utilities -------------------*- 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 is a configuration header for soft-float routines in compiler-rt.
  11 // This file does not provide any part of the compiler-rt interface, but defines
  12 // many useful constants and utility routines that are used in the
  13 // implementation of the soft-float routines in compiler-rt.
  14 //
  15 // Assumes that float and double correspond to the IEEE-754 binary32 and
  16 // binary64 types, respectively, and that integer endianness matches floating
  17 // point endianness on the target platform.
  18 //
  19 //===----------------------------------------------------------------------===//
  20
  21 #ifndef FP_LIB_HEADER
  22 #define FP_LIB_HEADER
  23
  24 #include <stdint.h>
  25 #include <stdbool.h>
  26 #include <limits.h>
  27 #include "int_lib.h"
  28
  29 #if defined SINGLE_PRECISION
  30
  31 typedef uint32_t rep_t;
  32 typedef int32_t srep_t;
  33 typedef float fp_t;
  34 #define REP_C UINT32_C
  35 #define significandBits 23
  36
  37 static inline int rep_clz(rep_t a) {
  38     return __builtin_clz(a);
  39 }
  40
  41 // 32x32 --> 64 bit multiply
  42 static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) {
  43     const uint64_t product = (uint64_t)a*b;
  44     *hi = product >> 32;
  45     *lo = product;
  46 }
  47
  48 #elif defined DOUBLE_PRECISION
  49
  50 typedef uint64_t rep_t;
  51 typedef int64_t srep_t;
  52 typedef double fp_t;
  53 #define REP_C UINT64_C
  54 #define significandBits 52
  55
  56 static inline int rep_clz(rep_t a) {
  57 #if defined __LP64__
  58     return __builtin_clzl(a);
  59 #else
  60     if (a & REP_C(0xffffffff00000000))
  61         return __builtin_clz(a >> 32);
  62     else
  63         return 32 + __builtin_clz(a & REP_C(0xffffffff));
  64 #endif
  65 }
  66
  67 #define loWord(a) (a & 0xffffffffU)
  68 #define hiWord(a) (a >> 32)
  69
  70 // 64x64 -> 128 wide multiply for platforms that don't have such an operation;
  71 // many 64-bit platforms have this operation, but they tend to have hardware
  72 // floating-point, so we don't bother with a special case for them here.
  73 static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) {
  74     // Each of the component 32x32 -> 64 products
  75     const uint64_t plolo = loWord(a) * loWord(b);
  76     const uint64_t plohi = loWord(a) * hiWord(b);
  77     const uint64_t philo = hiWord(a) * loWord(b);
  78     const uint64_t phihi = hiWord(a) * hiWord(b);
  79     // Sum terms that contribute to lo in a way that allows us to get the carry
  80     const uint64_t r0 = loWord(plolo);
  81     const uint64_t r1 = hiWord(plolo) + loWord(plohi) + loWord(philo);
  82     *lo = r0 + (r1 << 32);
  83     // Sum terms contributing to hi with the carry from lo
  84     *hi = hiWord(plohi) + hiWord(philo) + hiWord(r1) + phihi;
  85 }
  86
  87 #else
  88 #error Either SINGLE_PRECISION or DOUBLE_PRECISION must be defined.
  89 #endif
  90
  91 #define typeWidth       (sizeof(rep_t)*CHAR_BIT)
  92 #define exponentBits    (typeWidth - significandBits - 1)
  93 #define maxExponent     ((1 << exponentBits) - 1)
  94 #define exponentBias    (maxExponent >> 1)
  95
  96 #define implicitBit     (REP_C(1) << significandBits)
  97 #define significandMask (implicitBit - 1U)
  98 #define signBit         (REP_C(1) << (significandBits + exponentBits))
  99 #define absMask         (signBit - 1U)
 100 #define exponentMask    (absMask ^ significandMask)
 101 #define oneRep          ((rep_t)exponentBias << significandBits)
 102 #define infRep          exponentMask
 103 #define quietBit        (implicitBit >> 1)
 104 #define qnanRep         (exponentMask | quietBit)
 105
 106 static inline rep_t toRep(fp_t x) {
 107     const union { fp_t f; rep_t i; } rep = {.f = x};
 108     return rep.i;
 109 }
 110
 111 static inline fp_t fromRep(rep_t x) {
 112     const union { fp_t f; rep_t i; } rep = {.i = x};
 113     return rep.f;
 114 }
 115
 116 static inline int normalize(rep_t *significand) {
 117     const int shift = rep_clz(*significand) - rep_clz(implicitBit);
 118     *significand <<= shift;
 119     return 1 - shift;
 120 }
 121
 122 static inline void wideLeftShift(rep_t *hi, rep_t *lo, int count) {
 123     *hi = *hi << count | *lo >> (typeWidth - count);
 124     *lo = *lo << count;
 125 }
 126
 127 static inline void wideRightShiftWithSticky(rep_t *hi, rep_t *lo, unsigned int count) {
 128     if (count < typeWidth) {
 129         const bool sticky = *lo << (typeWidth - count);
 130         *lo = *hi << (typeWidth - count) | *lo >> count | sticky;
 131         *hi = *hi >> count;
 132     }
 133     else if (count < 2*typeWidth) {
 134         const bool sticky = *hi << (2*typeWidth - count) | *lo;
 135         *lo = *hi >> (count - typeWidth) | sticky;
 136         *hi = 0;
 137     } else {
 138         const bool sticky = *hi | *lo;
 139         *lo = sticky;
 140         *hi = 0;
 141     }
 142 }
 143
 144 #endif // FP_LIB_HEADER