1 /*
2  * Copyright 2008 The Android Open Source Project
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 
9 #ifndef SkFloatBits_DEFINED
10 #define SkFloatBits_DEFINED
11 
12 #include "SkTypes.h"
13 #include "SkSafe_math.h"
14 #include <float.h>
15 
16 /** Convert a sign-bit int (i.e. float interpreted as int) into a 2s compliement
17     int. This also converts -0 (0x80000000) to 0. Doing this to a float allows
18     it to be compared using normal C operators (<, <=, etc.)
19 */
20 static inline int32_t SkSignBitTo2sCompliment(int32_t x) {
21     if (x < 0) {
22         x &= 0x7FFFFFFF;
23         x = -x;
24     }
25     return x;
26 }
27 
28 /** Convert a 2s compliment int to a sign-bit (i.e. int interpreted as float).
29     This undoes the result of SkSignBitTo2sCompliment().
30  */
31 static inline int32_t Sk2sComplimentToSignBit(int32_t x) {
32     int sign = x >> 31;
33     // make x positive
34     x = (x ^ sign) - sign;
35     // set the sign bit as needed
36     x |= SkLeftShift(sign, 31);
37     return x;
38 }
39 
40 union SkFloatIntUnion {
41     float   fFloat;
42     int32_t fSignBitInt;
43 };
44 
45 // Helper to see a float as its bit pattern (w/o aliasing warnings)
46 static inline int32_t SkFloat2Bits(float x) {
47     SkFloatIntUnion data;
48     data.fFloat = x;
49     return data.fSignBitInt;
50 }
51 
52 // Helper to see a bit pattern as a float (w/o aliasing warnings)
53 static inline float SkBits2Float(int32_t floatAsBits) {
54     SkFloatIntUnion data;
55     data.fSignBitInt = floatAsBits;
56     return data.fFloat;
57 }
58 
59 /** Return the float as a 2s compliment int. Just to be used to compare floats
60     to each other or against positive float-bit-constants (like 0). This does
61     not return the int equivalent of the float, just something cheaper for
62     compares-only.
63  */
64 static inline int32_t SkFloatAs2sCompliment(float x) {
65     return SkSignBitTo2sCompliment(SkFloat2Bits(x));
66 }
67 
68 /** Return the 2s compliment int as a float. This undos the result of
69     SkFloatAs2sCompliment
70  */
71 static inline float Sk2sComplimentAsFloat(int32_t x) {
72     return SkBits2Float(Sk2sComplimentToSignBit(x));
73 }
74 
75 //  Scalar wrappers for float-bit routines
76 
77 #define SkScalarAs2sCompliment(x)    SkFloatAs2sCompliment(x)
78 
79 #endif
80