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/*
* Copyright 2011 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkClampRange.h"
/*
* returns [0..count] for the number of steps (<= count) for which x0 <= edge
* given each step is followed by x0 += dx
*/
static int chop(int64_t x0, SkFixed edge, int64_t x1, int64_t dx, int count) {
SkASSERT(dx > 0);
SkASSERT(count >= 0);
if (x0 >= edge) {
return 0;
}
if (x1 <= edge) {
return count;
}
int64_t n = (edge - x0 + dx - 1) / dx;
SkASSERT(n >= 0);
SkASSERT(n <= count);
return (int)n;
}
static bool overflows_fixed(int64_t x) {
return x < -SK_FixedMax || x > SK_FixedMax;
}
void SkClampRange::initFor1(SkFixed fx) {
fCount0 = fCount1 = fCount2 = 0;
if (fx <= 0) {
fCount0 = 1;
} else if (fx < 0xFFFF) {
fCount1 = 1;
fFx1 = fx;
} else {
fCount2 = 1;
}
}
void SkClampRange::init(SkFixed fx0, SkFixed dx0, int count, int v0, int v1) {
SkASSERT(count > 0);
fV0 = v0;
fV1 = v1;
// special case 1 == count, as it is slightly common for skia
// and avoids us ever calling divide or 64bit multiply
if (1 == count) {
this->initFor1(fx0);
return;
}
int64_t fx = fx0;
int64_t dx = dx0;
// start with ex equal to the last computed value
int64_t ex = fx + (count - 1) * dx;
if ((uint64_t)(fx | ex) <= 0xFFFF) {
fCount0 = fCount2 = 0;
fCount1 = count;
fFx1 = fx0;
return;
}
if (fx <= 0 && ex <= 0) {
fCount1 = fCount2 = 0;
fCount0 = count;
return;
}
if (fx >= 0xFFFF && ex >= 0xFFFF) {
fCount0 = fCount1 = 0;
fCount2 = count;
return;
}
int extraCount = 0;
// now make ex be 1 past the last computed value
ex += dx;
// now check for over/under flow
if (overflows_fixed(ex)) {
int originalCount = count;
int64_t ccount;
bool swap = dx < 0;
if (swap) {
dx = -dx;
fx = -fx;
}
ccount = (SK_FixedMax - fx + dx - 1) / dx;
if (swap) {
dx = -dx;
fx = -fx;
}
SkASSERT(ccount > 0 && ccount <= SK_FixedMax);
count = (int)ccount;
if (0 == count) {
this->initFor1(fx0);
if (dx > 0) {
fCount2 += originalCount - 1;
} else {
fCount0 += originalCount - 1;
}
return;
}
extraCount = originalCount - count;
ex = fx + dx * count;
}
bool doSwap = dx < 0;
if (doSwap) {
ex -= dx;
fx -= dx;
SkTSwap(fx, ex);
dx = -dx;
}
fCount0 = chop(fx, 0, ex, dx, count);
count -= fCount0;
fx += fCount0 * dx;
SkASSERT(fx >= 0);
SkASSERT(fCount0 == 0 || (fx - dx) < 0);
fCount1 = chop(fx, 0xFFFF, ex, dx, count);
count -= fCount1;
fCount2 = count;
#ifdef SK_DEBUG
fx += fCount1 * dx;
SkASSERT(fx <= ex);
if (fCount2 > 0) {
SkASSERT(fx >= 0xFFFF);
if (fCount1 > 0) {
SkASSERT(fx - dx < 0xFFFF);
}
}
#endif
if (doSwap) {
SkTSwap(fCount0, fCount2);
SkTSwap(fV0, fV1);
dx = -dx;
}
if (fCount1 > 0) {
fFx1 = fx0 + fCount0 * (int)dx;
}
if (dx > 0) {
fCount2 += extraCount;
} else {
fCount0 += extraCount;
}
}
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