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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"
#include "SkMathPriv.h"
static int SkCLZ64(uint64_t value) {
int count = 0;
if (value >> 32) {
value >>= 32;
} else {
count += 32;
}
return count + SkCLZ(SkToU32(value));
}
static bool sk_64_smul_check(int64_t count, int64_t dx, int64_t* result) {
// Do it the slow way until we have some assembly.
if (dx == std::numeric_limits<int64_t>::min()) {
return false; // SkTAbs overflow
}
SkASSERT(count >= 0);
uint64_t ucount = static_cast<uint64_t>(count);
uint64_t udx = static_cast<uint64_t>(SkTAbs(dx));
int zeros = SkCLZ64(ucount) + SkCLZ64(udx);
// this is a conservative check: it may return false when in fact it would not have overflowed.
// Hackers Delight uses 34 as its convervative check, but that is for 32x32 multiplies.
// Since we are looking at 64x64 muls, we add 32 to the check.
if (zeros < (32 + 34)) {
return false;
}
*result = count * dx;
return true;
}
static bool sk_64_sadd_check(int64_t a, int64_t b, int64_t* result) {
if (a > 0) {
if (b > std::numeric_limits<int64_t>::max() - a) {
return false;
}
} else {
if (b < std::numeric_limits<int64_t>::min() - a) {
return false;
}
}
*result = a + b;
return true;
}
/*
* 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, SkGradFixed 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;
}
void SkClampRange::initFor1(SkGradFixed fx) {
fCount0 = fCount1 = fCount2 = 0;
if (fx <= 0) {
fCount0 = 1;
} else if (fx < kFracMax_SkGradFixed) {
fCount1 = 1;
fFx1 = fx;
} else {
fCount2 = 1;
}
}
void SkClampRange::init(SkGradFixed fx0, SkGradFixed 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 count_times_dx, ex;
if (!sk_64_smul_check(count - 1, dx, &count_times_dx) ||
!sk_64_sadd_check(fx, count_times_dx, &ex)) {
// we can't represent the computed end in 32.32, so just draw something (first color)
fCount1 = fCount2 = 0;
fCount0 = count;
return;
}
if ((uint64_t)(fx | ex) <= kFracMax_SkGradFixed) {
fCount0 = fCount2 = 0;
fCount1 = count;
fFx1 = fx0;
return;
}
if (fx <= 0 && ex <= 0) {
fCount1 = fCount2 = 0;
fCount0 = count;
return;
}
if (fx >= kFracMax_SkGradFixed && ex >= kFracMax_SkGradFixed) {
fCount0 = fCount1 = 0;
fCount2 = count;
return;
}
// now make ex be 1 past the last computed value
ex += dx;
bool doSwap = dx < 0;
if (doSwap) {
ex -= dx;
fx -= dx;
SkTSwap(fx, ex);
dx = -dx;
}
fCount0 = chop(fx, 0, ex, dx, count);
SkASSERT(fCount0 >= 0);
SkASSERT(fCount0 <= count);
count -= fCount0;
fx += fCount0 * dx;
SkASSERT(fx >= 0);
SkASSERT(fCount0 == 0 || (fx - dx) < 0);
fCount1 = chop(fx, kFracMax_SkGradFixed, ex, dx, count);
SkASSERT(fCount1 >= 0);
SkASSERT(fCount1 <= count);
count -= fCount1;
fCount2 = count;
#ifdef SK_DEBUG
fx += fCount1 * dx;
SkASSERT(fx <= ex);
if (fCount2 > 0) {
SkASSERT(fx >= kFracMax_SkGradFixed);
if (fCount1 > 0) {
SkASSERT(fx - dx < kFracMax_SkGradFixed);
}
}
#endif
if (doSwap) {
SkTSwap(fCount0, fCount2);
SkTSwap(fV0, fV1);
dx = -dx;
}
if (fCount1 > 0) {
fFx1 = fx0 + fCount0 * dx;
}
}
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