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lzw: Adapt main code handling to handle clear codes too.

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Michael Drake 2021-04-03 22:11:58 +01:00 committed by Michael Drake
parent 367f64c5bc
commit 64ddf20599
1 changed files with 25 additions and 53 deletions
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62
libvips/foreign/libnsgif/lzw.c
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@ -226,39 +226,13 @@ static inline lzw_result lzw__read_code(
* \param[in] ctx LZW reading context, updated. * \param[in] ctx LZW reading context, updated.
* \return LZW_OK or error code. * \return LZW_OK or error code.
*/ */
static lzw_result lzw__clear_codes( static inline void lzw__clear_table(
struct lzw_ctx *ctx) struct lzw_ctx *ctx)
{ {
uint32_t code;
/* Reset table building context */ /* Reset table building context */
ctx->code_size = ctx->initial_code_size; ctx->code_size = ctx->initial_code_size;
ctx->code_max = (1 << ctx->initial_code_size) - 1; ctx->code_max = (1 << ctx->initial_code_size) - 1;
ctx->table_size = ctx->eoi_code + 1; ctx->table_size = ctx->eoi_code + 1;
/* There might be a sequence of clear codes, so process them all */
do {
lzw_result res = lzw__read_code(&ctx->input,
ctx->code_size, &code);
if (res != LZW_OK) {
return res;
}
} while (code == ctx->clear_code);
/* The initial code must be from the initial table. */
if (code > ctx->clear_code) {
return LZW_BAD_ICODE;
}
/* 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. */
ctx->stack_base[ctx->written++] = code;
return LZW_OK;
} }
@ -298,10 +272,11 @@ lzw_result lzw_decode_init(
table[i].count = 1; table[i].count = 1;
} }
ctx->written = 0; lzw__clear_table(ctx);
ctx->prev_code = ctx->clear_code;
*stack_base_out = ctx->stack_base; *stack_base_out = ctx->stack_base;
return lzw__clear_codes(ctx); return LZW_OK;
} }
/** /**
@ -355,6 +330,8 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
lzw_result res; lzw_result res;
uint32_t code; uint32_t code;
ctx->written = 0;
/* Get a new code from the input */ /* Get a new code from the input */
res = lzw__read_code(&ctx->input, ctx->code_size, &code); res = lzw__read_code(&ctx->input, ctx->code_size, &code);
if (res != LZW_OK) { if (res != LZW_OK) {
@ -362,46 +339,41 @@ lzw_result lzw_decode(struct lzw_ctx *ctx,
} }
/* Handle the new code */ /* Handle the new code */
if (code == ctx->clear_code) { if (code == ctx->eoi_code) {
/* Got Clear code */
res = lzw__clear_codes(ctx);
if (res == LZW_OK) {
*written = ctx->written;
ctx->written = 0;
}
return res;
} else if (code == ctx->eoi_code) {
/* Got End of Information code */ /* Got End of Information code */
return LZW_EOI_CODE; return LZW_EOI_CODE;
} else if (code > ctx->table_size) { } else if (code > ctx->table_size) {
/* Code is invalid */ /* Code is invalid */
return LZW_BAD_CODE; return LZW_BAD_CODE;
}
if (ctx->table_size < LZW_TABLE_ENTRY_MAX) { } else if (code == ctx->clear_code) {
lzw__clear_table(ctx);
} else {
if (ctx->prev_code != ctx->clear_code &&
ctx->table_size < LZW_TABLE_ENTRY_MAX) {
uint32_t size = ctx->table_size; uint32_t size = ctx->table_size;
lzw__table_add_entry(ctx, (code < size) ? lzw__table_add_entry(ctx, (code < size) ?
ctx->table[code].first : ctx->table[code].first :
ctx->prev_code_first); ctx->prev_code_first);
/* Ensure code size is increased, if needed. */ /* Ensure code size is increased, if needed. */
if (size == ctx->code_max && ctx->code_size < LZW_CODE_MAX) { if (size == ctx->code_max &&
ctx->code_size < LZW_CODE_MAX) {
ctx->code_size++; ctx->code_size++;
ctx->code_max = (1 << ctx->code_size) - 1; ctx->code_max = (1 << ctx->code_size) - 1;
} }
} }
lzw__write_pixels(ctx, code);
}
/* Store details of this code as "previous code" to the context. */ /* Store details of this code as "previous code" to the context. */
ctx->prev_code_first = ctx->table[code].first; ctx->prev_code_first = ctx->table[code].first;
ctx->prev_code_count = ctx->table[code].count; ctx->prev_code_count = ctx->table[code].count;
ctx->prev_code = code; ctx->prev_code = code;
lzw__write_pixels(ctx, code);
*written = ctx->written; *written = ctx->written;
ctx->written = 0;
return LZW_OK; return LZW_OK;
} }