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
rep_clz(rep_t a)37 static inline int rep_clz(rep_t a) {
38 return __builtin_clz(a);
39 }
40
41 // 32x32 --> 64 bit multiply
wideMultiply(rep_t a,rep_t b,rep_t * hi,rep_t * lo)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
rep_clz(rep_t a)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.
wideMultiply(rep_t a,rep_t b,rep_t * hi,rep_t * lo)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
toRep(fp_t x)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
fromRep(rep_t x)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
normalize(rep_t * significand)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
wideLeftShift(rep_t * hi,rep_t * lo,int count)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
wideRightShiftWithSticky(rep_t * hi,rep_t * lo,unsigned int count)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
145