-static const uint16_t mask[17] =
-{
- 0x0000, 0x0001, 0x0003, 0x0007,
- 0x000F, 0x001F, 0x003F, 0x007F,
- 0x00FF, 0x01FF, 0x03FF, 0x07FF,
- 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
-};
-
-static void GLZWDecodeInit(GifState * s, int csize)
-{
- /* read buffer */
- s->eob_reached = 0;
- s->pbuf = s->buf;
- s->ebuf = s->buf;
- s->bbuf = 0;
- s->bbits = 0;
-
- /* decoder */
- s->codesize = csize;
- s->cursize = s->codesize + 1;
- s->curmask = mask[s->cursize];
- s->top_slot = 1 << s->cursize;
- s->clear_code = 1 << s->codesize;
- s->end_code = s->clear_code + 1;
- s->slot = s->newcodes = s->clear_code + 2;
- s->oc = s->fc = 0;
- s->sp = s->stack;
-}
-
-/* XXX: optimize */
-static inline int GetCode(GifState * s)
-{
- int c, sizbuf;
- uint8_t *ptr;
-
- while (s->bbits < s->cursize) {
- ptr = s->pbuf;
- if (ptr >= s->ebuf) {
- if (!s->eob_reached) {
- sizbuf = bytestream_get_byte(&s->bytestream);
- s->ebuf = s->buf + sizbuf;
- s->pbuf = s->buf;
- if (sizbuf > 0) {
- bytestream_get_buffer(&s->bytestream, s->buf, sizbuf);
- } else {
- s->eob_reached = 1;
- }
- }
- ptr = s->pbuf;
- }
- s->bbuf |= ptr[0] << s->bbits;
- ptr++;
- s->pbuf = ptr;
- s->bbits += 8;
- }
- c = s->bbuf & s->curmask;
- s->bbuf >>= s->cursize;
- s->bbits -= s->cursize;
- return c;
-}
-
-/* NOTE: the algorithm here is inspired from the LZW GIF decoder
- written by Steven A. Bennett in 1987. */
-/* return the number of byte decoded */
-static int GLZWDecode(GifState * s, uint8_t * buf, int len)
-{
- int l, c, code, oc, fc;
- uint8_t *sp;
-
- if (s->end_code < 0)
- return 0;
-
- l = len;
- sp = s->sp;
- oc = s->oc;
- fc = s->fc;
-
- while (sp > s->stack) {
- *buf++ = *(--sp);
- if ((--l) == 0)
- goto the_end;
- }
-
- for (;;) {
- c = GetCode(s);
- if (c == s->end_code) {
- s->end_code = -1;
- break;
- } else if (c == s->clear_code) {
- s->cursize = s->codesize + 1;
- s->curmask = mask[s->cursize];
- s->slot = s->newcodes;
- s->top_slot = 1 << s->cursize;
- while ((c = GetCode(s)) == s->clear_code);
- if (c == s->end_code) {
- s->end_code = -1;
- break;
- }
- /* test error */
- if (c >= s->slot)
- c = 0;
- fc = oc = c;
- *buf++ = c;
- if ((--l) == 0)
- break;
- } else {
- code = c;
- if (code >= s->slot) {
- *sp++ = fc;
- code = oc;
- }
- while (code >= s->newcodes) {
- *sp++ = s->suffix[code];
- code = s->prefix[code];
- }
- *sp++ = code;
- if (s->slot < s->top_slot) {
- s->suffix[s->slot] = fc = code;
- s->prefix[s->slot++] = oc;
- oc = c;
- }
- if (s->slot >= s->top_slot) {
- if (s->cursize < MAXBITS) {
- s->top_slot <<= 1;
- s->curmask = mask[++s->cursize];
- }
- }
- while (sp > s->stack) {
- *buf++ = *(--sp);
- if ((--l) == 0)
- goto the_end;
- }
- }
- }
- the_end:
- s->sp = sp;
- s->oc = oc;
- s->fc = fc;
- return len - l;
-}
-