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/*
* Copyright 2006 The Android Open Source Project
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkFDot6_DEFINED
#define SkFDot6_DEFINED
#include "SkFixed.h"
#include "SkMath.h"
#include "SkScalar.h"
#include "SkTo.h"
typedef int32_t SkFDot6;
/* This uses the magic number approach suggested here:
* http://stereopsis.com/sree/fpu2006.html and used in
* _cairo_fixed_from_double. It does banker's rounding
* (i.e. round to nearest even)
*/
inline SkFDot6 SkScalarRoundToFDot6(SkScalar x, int shift = 0)
{
union {
double fDouble;
int32_t fBits[2];
} tmp;
int fractionalBits = 6 + shift;
double magic = (1LL << (52 - (fractionalBits))) * 1.5;
tmp.fDouble = SkScalarToDouble(x) + magic;
#ifdef SK_CPU_BENDIAN
return tmp.fBits[1];
#else
return tmp.fBits[0];
#endif
}
#define SK_FDot6One (64)
#define SK_FDot6Half (32)
#ifdef SK_DEBUG
inline SkFDot6 SkIntToFDot6(S16CPU x) {
SkASSERT(SkToS16(x) == x);
return x << 6;
}
#else
#define SkIntToFDot6(x) ((x) << 6)
#endif
#define SkFDot6Floor(x) ((x) >> 6)
#define SkFDot6Ceil(x) (((x) + 63) >> 6)
#define SkFDot6Round(x) (((x) + 32) >> 6)
#define SkFixedToFDot6(x) ((x) >> 10)
inline SkFixed SkFDot6ToFixed(SkFDot6 x) {
SkASSERT((SkLeftShift(x, 10) >> 10) == x);
return SkLeftShift(x, 10);
}
#define SkScalarToFDot6(x) (SkFDot6)((x) * 64)
#define SkFDot6ToScalar(x) ((SkScalar)(x) * 0.015625f)
#define SkFDot6ToFloat SkFDot6ToScalar
inline SkFixed SkFDot6Div(SkFDot6 a, SkFDot6 b) {
SkASSERT(b != 0);
if (a == (int16_t)a) {
return SkLeftShift(a, 16) / b;
} else {
return SkFixedDiv(a, b);
}
}
#include "SkFDot6Constants.h"
class QuickFDot6Inverse {
public:
inline static SkFixed Lookup(SkFDot6 x) {
SkASSERT(SkAbs32(x) < kInverseTableSize);
return gFDot6INVERSE[kInverseTableSize + x];
}
};
static inline SkFixed QuickSkFDot6Div(SkFDot6 a, SkFDot6 b) {
const int kMinBits = 3; // abs(b) should be at least (1 << kMinBits) for quick division
const int kMaxBits = 31; // Number of bits available in signed int
// Given abs(b) <= (1 << kMinBits), the inverse of abs(b) is at most 1 << (22 - kMinBits) in
// SkFixed format. Hence abs(a) should be less than kMaxAbsA
const int kMaxAbsA = 1 << (kMaxBits - (22 - kMinBits));
SkFDot6 abs_a = SkAbs32(a);
SkFDot6 abs_b = SkAbs32(b);
if (abs_b >= (1 << kMinBits) && abs_b < kInverseTableSize && abs_a < kMaxAbsA) {
SkASSERT((int64_t)a * QuickFDot6Inverse::Lookup(b) <= SK_MaxS32
&& (int64_t)a * QuickFDot6Inverse::Lookup(b) >= SK_MinS32);
SkFixed ourAnswer = (a * QuickFDot6Inverse::Lookup(b)) >> 6;
#ifdef SK_DEBUG
SkFixed directAnswer = SkFDot6Div(a, b);
SkASSERT(
(directAnswer == 0 && ourAnswer == 0) ||
SkFixedDiv(SkAbs32(directAnswer - ourAnswer), SkAbs32(directAnswer)) <= 1 << 10
);
#endif
return ourAnswer;
} else {
return SkFDot6Div(a, b);
}
}
#endif
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