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lzw: Store code's value count in table.

This commit is contained in:
Michael Drake 2021-04-02 22:19:42 +01:00 committed by Michael Drake
parent 8d8aa0dd46
commit 06443e64e9
1 changed files with 6 additions and 0 deletions
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6
libvips/foreign/libnsgif/lzw.c
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@ -58,6 +58,7 @@ struct lzw_read_ctx {
struct lzw_table_entry {
uint8_t value; /**< Last value for record ending at entry. */
uint8_t first; /**< First value in entry's entire record. */
uint16_t count; /**< Count of values in this entry's record. */
uint16_t extends; /**< Offset in table to previous entry. */
};
@ -69,6 +70,7 @@ struct lzw_ctx {
uint32_t prev_code; /**< Code read from input previously. */
uint32_t prev_code_first; /**< First value of previous code. */
uint32_t prev_code_count; /**< Total values for previous code. */
uint32_t initial_code_size; /**< Starting LZW code size. */
@ -253,6 +255,7 @@ static lzw_result lzw__clear_codes(
/* Record this initial code as "previous" code, needed during decode. */
ctx->prev_code = code;
ctx->prev_code_first = code;
ctx->prev_code_count = 1;
/* Reset the stack, and add first non-clear code added as first item. */
stack_pos = ctx->stack_base;
@ -297,6 +300,7 @@ lzw_result lzw_decode_init(
for (uint32_t i = 0; i < ctx->clear_code; ++i) {
table[i].first = i;
table[i].value = i;
table[i].count = 1;
}
*stack_base_out = ctx->stack_base;
@ -317,6 +321,7 @@ static inline void lzw__table_add_entry(
entry->value = code;
entry->first = ctx->prev_code_first;
entry->count = ctx->prev_code_count + 1;
entry->extends = ctx->prev_code;
ctx->table_size++;
@ -392,6 +397,7 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
/* Store details of this code as "previous code" to the context. */
ctx->prev_code_first = ctx->table[code].first;
ctx->prev_code_count = ctx->table[code].count;
ctx->prev_code = code;
lzw__write_pixels(ctx, code, stack_pos_out);