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lzw: Simplify new code handling. 

The tiny overhead of an extra time through the output loop
is worth the simpler code.
This commit is contained in:
Michael Drake 2021-03-31 19:04:02 +01:00 committed by Michael Drake
parent 21c565d5d6
commit f66e20e017
1 changed files with 6 additions and 11 deletions
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17
libvips/foreign/libnsgif/lzw.c
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@ -4,6 +4,7 @@
* http://www.opensource.org/licenses/mit-license.php
*
* Copyright 2017 Michael Drake <michael.drake@codethink.co.uk>
* Copyright 2021 Michael Drake <tlsa@netsurf-browser.org>
*/
#include <assert.h>
@ -307,7 +308,6 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
{
lzw_result res;
uint32_t code_new;
uint32_t code_out;
uint8_t last_value;
uint8_t *stack_pos = ctx->stack_base;
uint32_t clear_code = ctx->clear_code;
@ -335,12 +335,9 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
} else if (code_new < current_entry) {
/* Code is in table */
code_out = code_new;
last_value = table[code_new].first_value;
} else {
/* Code not in table */
*stack_pos++ = ctx->previous_code_first;
code_out = ctx->previous_code;
last_value = ctx->previous_code_first;
}
@ -366,15 +363,13 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
ctx->previous_code_first = table[code_new].first_value;
ctx->previous_code = code_new;
/* Put rest of data for this code on output stack.
* Note, in the case of "code not in table", the last entry of the
* current code has already been placed on the stack above. */
while (code_out > clear_code) {
struct lzw_dictionary_entry *entry = table + code_out;
/* Put data for this code on output stack. */
while (code_new > clear_code) {
struct lzw_dictionary_entry *entry = table + code_new;
*stack_pos++ = entry->last_value;
code_out = entry->previous_entry;
code_new = entry->previous_entry;
}
*stack_pos++ = table[code_out].last_value;
*stack_pos++ = table[code_new].last_value;
*stack_pos_out = stack_pos;
return LZW_OK;