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comparison: gfx/skia/trunk/src/core/SkFloatBits.cpp

gfx/skia/trunk/src/core/SkFloatBits.cpp

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1 /*
2 * Copyright 2011 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "SkFloatBits.h"
9 #include "SkMathPriv.h"
10
11 /******************************************************************************
12 SkFloatBits_toInt[Floor, Round, Ceil] are identical except for what they
13 do right before they return ... >> exp;
14 Floor - adds nothing
15 Round - adds 1 << (exp - 1)
16 Ceil - adds (1 << exp) - 1
17
18 Floor and Cast are very similar, but Cast applies its sign after all other
19 computations on value. Also, Cast does not need to check for negative zero,
20 as that value (0x80000000) "does the right thing" for Ceil. Note that it
21 doesn't for Floor/Round/Ceil, hence the explicit check.
22 ******************************************************************************/
23
24 #define EXP_BIAS (127+23)
25 #define MATISSA_MAGIC_BIG (1 << 23)
26
27 static inline int unpack_exp(uint32_t packed) {
28 return (packed << 1 >> 24);
29 }
30
31 #if 0
32 // the ARM compiler generates an extra BIC, so I use the dirty version instead
33 static inline int unpack_matissa(uint32_t packed) {
34 // we could mask with 0x7FFFFF, but that is harder for ARM to encode
35 return (packed & ~0xFF000000) | MATISSA_MAGIC_BIG;
36 }
37 #endif
38
39 // returns the low 24-bits, so we need to OR in the magic_bit afterwards
40 static inline int unpack_matissa_dirty(uint32_t packed) {
41 return packed & ~0xFF000000;
42 }
43
44 // same as (int)float
45 int32_t SkFloatBits_toIntCast(int32_t packed) {
46 int exp = unpack_exp(packed) - EXP_BIAS;
47 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
48
49 if (exp >= 0) {
50 if (exp > 7) { // overflow
51 value = SK_MaxS32;
52 } else {
53 value <<= exp;
54 }
55 } else {
56 exp = -exp;
57 if (exp > 25) { // underflow
58 exp = 25;
59 }
60 value >>= exp;
61 }
62 return SkApplySign(value, SkExtractSign(packed));
63 }
64
65 // same as (int)floor(float)
66 int32_t SkFloatBits_toIntFloor(int32_t packed) {
67 // curse you negative 0
68 if ((packed << 1) == 0) {
69 return 0;
70 }
71
72 int exp = unpack_exp(packed) - EXP_BIAS;
73 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
74
75 if (exp >= 0) {
76 if (exp > 7) { // overflow
77 value = SK_MaxS32;
78 } else {
79 value <<= exp;
80 }
81 // apply the sign after we check for overflow
82 return SkApplySign(value, SkExtractSign(packed));
83 } else {
84 // apply the sign before we right-shift
85 value = SkApplySign(value, SkExtractSign(packed));
86 exp = -exp;
87 if (exp > 25) { // underflow
88 exp = 25;
89 }
90 // int add = 0;
91 return value >> exp;
92 }
93 }
94
95 // same as (int)floor(float + 0.5)
96 int32_t SkFloatBits_toIntRound(int32_t packed) {
97 // curse you negative 0
98 if ((packed << 1) == 0) {
99 return 0;
100 }
101
102 int exp = unpack_exp(packed) - EXP_BIAS;
103 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
104
105 if (exp >= 0) {
106 if (exp > 7) { // overflow
107 value = SK_MaxS32;
108 } else {
109 value <<= exp;
110 }
111 // apply the sign after we check for overflow
112 return SkApplySign(value, SkExtractSign(packed));
113 } else {
114 // apply the sign before we right-shift
115 value = SkApplySign(value, SkExtractSign(packed));
116 exp = -exp;
117 if (exp > 25) { // underflow
118 exp = 25;
119 }
120 int add = 1 << (exp - 1);
121 return (value + add) >> exp;
122 }
123 }
124
125 // same as (int)ceil(float)
126 int32_t SkFloatBits_toIntCeil(int32_t packed) {
127 // curse you negative 0
128 if ((packed << 1) == 0) {
129 return 0;
130 }
131
132 int exp = unpack_exp(packed) - EXP_BIAS;
133 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
134
135 if (exp >= 0) {
136 if (exp > 7) { // overflow
137 value = SK_MaxS32;
138 } else {
139 value <<= exp;
140 }
141 // apply the sign after we check for overflow
142 return SkApplySign(value, SkExtractSign(packed));
143 } else {
144 // apply the sign before we right-shift
145 value = SkApplySign(value, SkExtractSign(packed));
146 exp = -exp;
147 if (exp > 25) { // underflow
148 exp = 25;
149 }
150 int add = (1 << exp) - 1;
151 return (value + add) >> exp;
152 }
153 }
154
155 float SkIntToFloatCast(int32_t value) {
156 if (0 == value) {
157 return 0;
158 }
159
160 int shift = EXP_BIAS;
161
162 // record the sign and make value positive
163 int sign = SkExtractSign(value);
164 value = SkApplySign(value, sign);
165
166 if (value >> 24) { // value is too big (has more than 24 bits set)
167 int bias = 8 - SkCLZ(value);
168 SkDebugf("value = %d, bias = %d\n", value, bias);
169 SkASSERT(bias > 0 && bias < 8);
170 value >>= bias; // need to round?
171 shift += bias;
172 } else {
173 int zeros = SkCLZ(value << 8);
174 SkASSERT(zeros >= 0 && zeros <= 23);
175 value <<= zeros;
176 shift -= zeros;
177 }
178
179 // now value is left-aligned to 24 bits
180 SkASSERT((value >> 23) == 1);
181 SkASSERT(shift >= 0 && shift <= 255);
182
183 SkFloatIntUnion data;
184 data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG);
185 return data.fFloat;
186 }
187
188 float SkIntToFloatCast_NoOverflowCheck(int32_t value) {
189 if (0 == value) {
190 return 0;
191 }
192
193 int shift = EXP_BIAS;
194
195 // record the sign and make value positive
196 int sign = SkExtractSign(value);
197 value = SkApplySign(value, sign);
198
199 int zeros = SkCLZ(value << 8);
200 value <<= zeros;
201 shift -= zeros;
202
203 SkFloatIntUnion data;
204 data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG);
205 return data.fFloat;
206 }

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