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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 "SkPackBits.h"
#include "SkTo.h"
#include <cstring>
size_t SkPackBits::ComputeMaxSize8(size_t srcSize) {
// worst case is the number of 8bit values + 1 byte per (up to) 128 entries.
return ((srcSize + 127) >> 7) + srcSize;
}
static uint8_t* flush_same8(uint8_t dst[], uint8_t value, size_t count) {
while (count > 0) {
size_t n = count > 128 ? 128 : count;
*dst++ = (uint8_t)(n - 1);
*dst++ = (uint8_t)value;
count -= n;
}
return dst;
}
static uint8_t* flush_diff8(uint8_t* SK_RESTRICT dst,
const uint8_t* SK_RESTRICT src, size_t count) {
while (count > 0) {
size_t n = count > 128 ? 128 : count;
*dst++ = (uint8_t)(n + 127);
memcpy(dst, src, n);
src += n;
dst += n;
count -= n;
}
return dst;
}
size_t SkPackBits::Pack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
uint8_t* SK_RESTRICT dst, size_t dstSize) {
if (dstSize < ComputeMaxSize8(srcSize)) {
return 0;
}
uint8_t* const origDst = dst;
const uint8_t* stop = src + srcSize;
for (intptr_t count = stop - src; count > 0; count = stop - src) {
if (1 == count) {
*dst++ = 0;
*dst++ = *src;
break;
}
unsigned value = *src;
const uint8_t* s = src + 1;
if (*s == value) { // accumulate same values...
do {
s++;
if (s == stop) {
break;
}
} while (*s == value);
dst = flush_same8(dst, value, SkToInt(s - src));
} else { // accumulate diff values...
do {
if (++s == stop) {
goto FLUSH_DIFF;
}
// only stop if we hit 3 in a row,
// otherwise we get bigger than compuatemax
} while (*s != s[-1] || s[-1] != s[-2]);
s -= 2; // back up so we don't grab the "same" values that follow
FLUSH_DIFF:
dst = flush_diff8(dst, src, SkToInt(s - src));
}
src = s;
}
return dst - origDst;
}
int SkPackBits::Unpack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
uint8_t* SK_RESTRICT dst, size_t dstSize) {
uint8_t* const origDst = dst;
uint8_t* const endDst = dst + dstSize;
const uint8_t* stop = src + srcSize;
while (src < stop) {
unsigned n = *src++;
if (n <= 127) { // repeat count (n + 1)
n += 1;
if (dst > (endDst - n) || src >= stop) {
return 0;
}
memset(dst, *src++, n);
} else { // same count (n - 127)
n -= 127;
if (dst > (endDst - n) || src > (stop - n)) {
return 0;
}
memcpy(dst, src, n);
src += n;
}
dst += n;
}
SkASSERT(src <= stop);
SkASSERT(dst <= endDst);
return SkToInt(dst - origDst);
}
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