1 /*
2  * Copyright 2006 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 #ifndef SkFDot6_DEFINED
9 #define SkFDot6_DEFINED
10 
11 #include "SkFixed.h"
12 #include "SkMath.h"
13 #include "SkScalar.h"
14 #include "SkTo.h"
15 
16 typedef int32_t SkFDot6;
17 
18 /* This uses the magic number approach suggested here:
19  * http://stereopsis.com/sree/fpu2006.html and used in
20  * _cairo_fixed_from_double. It does banker's rounding
21  * (i.e. round to nearest even)
22  */
23 inline SkFDot6 SkScalarRoundToFDot6(SkScalar x, int shift = 0)
24 {
25     union {
26         double  fDouble;
27         int32_t fBits[2];
28     } tmp;
29     int fractionalBits = 6 + shift;
30     double magic = (1LL << (52 - (fractionalBits))) * 1.5;
31 
32     tmp.fDouble = SkScalarToDouble(x) + magic;
33 #ifdef SK_CPU_BENDIAN
34     return tmp.fBits[1];
35 #else
36     return tmp.fBits[0];
37 #endif
38 }
39 
40 #define SK_FDot6One         (64)
41 #define SK_FDot6Half        (32)
42 
43 #ifdef SK_DEBUG
SkIntToFDot6(int x)44     inline SkFDot6 SkIntToFDot6(int x) {
45         SkASSERT(SkToS16(x) == x);
46         return x << 6;
47     }
48 #else
49     #define SkIntToFDot6(x) ((x) << 6)
50 #endif
51 
52 #define SkFDot6Floor(x)     ((x) >> 6)
53 #define SkFDot6Ceil(x)      (((x) + 63) >> 6)
54 #define SkFDot6Round(x)     (((x) + 32) >> 6)
55 
56 #define SkFixedToFDot6(x)   ((x) >> 10)
57 
SkFDot6ToFixed(SkFDot6 x)58 inline SkFixed SkFDot6ToFixed(SkFDot6 x) {
59     SkASSERT((SkLeftShift(x, 10) >> 10) == x);
60 
61     return SkLeftShift(x, 10);
62 }
63 
64 #define SkScalarToFDot6(x)  (SkFDot6)((x) * 64)
65 #define SkFDot6ToScalar(x)  ((SkScalar)(x) * 0.015625f)
66 #define SkFDot6ToFloat      SkFDot6ToScalar
67 
SkFDot6Div(SkFDot6 a,SkFDot6 b)68 inline SkFixed SkFDot6Div(SkFDot6 a, SkFDot6 b) {
69     SkASSERT(b != 0);
70 
71     if (a == (int16_t)a) {
72         return SkLeftShift(a, 16) / b;
73     } else {
74         return SkFixedDiv(a, b);
75     }
76 }
77 
78 #endif
79