mirror of
https://github.com/nzbget/nzbget.git
synced 2026-06-14 14:44:14 -04:00
#454: one-pass simd decoder
updated SIMD decoder, support for end-of-stream detection
This commit is contained in:
Andrey Prygunkov
@@ -22,8 +22,7 @@
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#include "nzbget.h"
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namespace YEncode
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{
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#include "YEncode.h"
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// combine two 8-bit ints into a 16-bit one
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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@@ -32,55 +31,135 @@ namespace YEncode
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#define UINT16_PACK(a, b) (((a) << 8) | (b))
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#endif
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// state var: refers to the previous state - only used for incremental processing
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// 0: previous characters are `\r\n` OR there is no previous character
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// 1: previous character is `=`
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// 2: previous character is `\r`
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// 3: previous character is none of the above
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size_t decode_scalar(const unsigned char* src, unsigned char* dest, size_t len, char* state) {
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unsigned char *es = (unsigned char*)src + len; // end source pointer
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unsigned char *p = dest; // destination pointer
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namespace YEncode
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{
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// return values:
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// - 0: no end sequence found
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// - 1: \r\n=y sequence found, src points to byte after 'y'
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// - 2: \r\n.\r\n sequence found, src points to byte after last '\n'
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int decode_scalar(const unsigned char** src, unsigned char** dest, size_t len, YencDecoderState* state) {
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const unsigned char *es = (*src) + len; // end source pointer
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unsigned char *p = *dest; // destination pointer
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long i = -(long)len; // input position
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unsigned char c; // input character
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if (len < 1) return 0;
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if (state) switch (*state) {
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case 1:
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if(len < 1) return 0;
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#define YDEC_CHECK_END(s) if(i == 0) { \
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*state = s; \
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*src = es; \
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*dest = p; \
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return 0; \
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}
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if(state) switch(*state) {
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case YDEC_STATE_CRLFEQ: do_decode_endable_scalar_ceq:
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if(es[i] == 'y') {
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*state = YDEC_STATE_NONE;
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*src = es+i+1;
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*dest = p;
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return 1;
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} // else fall thru and escape
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case YDEC_STATE_EQ:
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c = es[i];
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*p++ = c - 42 - 64;
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i++;
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if (c == '\r' && i < 0) {
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*state = 2;
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// fall through to case 2
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}
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else {
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*state = 3;
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break;
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}
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case 2:
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if (es[i] != '\n') break;
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if(c != '\r') break;
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YDEC_CHECK_END(YDEC_STATE_CR)
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// fall through
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case YDEC_STATE_CR:
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if(es[i] != '\n') break;
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i++;
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*state = 0; // now `\r\n`
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if (i >= 0) return 0;
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case 0:
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// skip past first dot
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if (es[i] == '.') i++;
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}
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else // treat as *state == 0
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if (es[i] == '.') i++;
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for (; i < -2; i++) {
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YDEC_CHECK_END(YDEC_STATE_CRLF)
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case YDEC_STATE_CRLF: do_decode_endable_scalar_c0:
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if(es[i] == '.') {
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFDT)
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// fallthru
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} else if(es[i] == '=') {
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFEQ)
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goto do_decode_endable_scalar_ceq;
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} else
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break;
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case YDEC_STATE_CRLFDT:
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if(es[i] == '\r') {
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFDTCR)
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// fallthru
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} else if(es[i] == '=') { // check for dot-stuffed ending: \r\n.=y
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFEQ)
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goto do_decode_endable_scalar_ceq;
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} else
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break;
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case YDEC_STATE_CRLFDTCR:
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if(es[i] == '\n') {
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*state = YDEC_STATE_CRLF;
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*src = es + i + 1;
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*dest = p;
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return 2;
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} else
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break;
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case YDEC_STATE_NONE: break; // silence compiler warning
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} else // treat as YDEC_STATE_CRLF
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goto do_decode_endable_scalar_c0;
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for(; i < -2; i++) {
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c = es[i];
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switch (c) {
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case '\r':
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// skip past \r\n. sequences
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if (*(uint16_t*)(es + i + 1) == UINT16_PACK('\n', '.'))
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i += 2;
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case '\n':
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switch(c) {
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case '\r': {
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uint16_t next = *(uint16_t*)(es + i + 1);
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if(next == UINT16_PACK('\n', '.')) {
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// skip past \r\n. sequences
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i += 3;
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YDEC_CHECK_END(YDEC_STATE_CRLFDT)
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// check for end
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if(es[i] == '\r') {
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFDTCR)
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if(es[i] == '\n') {
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*src = es + i + 1;
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*dest = p;
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*state = YDEC_STATE_CRLF;
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return 2;
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} else i--;
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} else if(es[i] == '=') {
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i++;
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YDEC_CHECK_END(YDEC_STATE_CRLFEQ)
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if(es[i] == 'y') {
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*src = es + i + 1;
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*dest = p;
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*state = YDEC_STATE_NONE;
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return 1;
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} else {
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// escape char & continue
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c = es[i];
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*p++ = c - 42 - 64;
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i -= (c == '\r');
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}
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} else i--;
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}
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else if(next == UINT16_PACK('\n', '=')) {
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i += 3;
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YDEC_CHECK_END(YDEC_STATE_CRLFEQ)
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if(es[i] == 'y') {
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// ended
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*src = es + i + 1;
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*dest = p;
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*state = YDEC_STATE_NONE;
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return 1;
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} else {
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// escape char & continue
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c = es[i];
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*p++ = c - 42 - 64;
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i -= (c == '\r');
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}
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}
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} case '\n':
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continue;
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case '=':
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c = es[i + 1];
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c = es[i+1];
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*p++ = c - 42 - 64;
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i += (c != '\r'); // if we have a \r, reprocess character to deal with \r\n. case
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continue;
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@@ -88,20 +167,22 @@ size_t decode_scalar(const unsigned char* src, unsigned char* dest, size_t len,
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*p++ = c - 42;
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}
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}
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if (state) *state = 3;
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if (i == -2) { // 2nd last char
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if(state) *state = YDEC_STATE_NONE;
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if(i == -2) { // 2nd last char
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c = es[i];
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switch (c) {
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switch(c) {
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case '\r':
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if (state && es[i + 1] == '\n') {
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*state = 0;
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return p - dest;
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if(state && es[i+1] == '\n') {
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*state = YDEC_STATE_CRLF;
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*src = es;
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*dest = p;
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return 0;
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}
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case '\n':
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break;
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case '=':
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c = es[i + 1];
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c = es[i+1];
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*p++ = c - 42 - 64;
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i += (c != '\r');
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break;
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@@ -110,21 +191,27 @@ size_t decode_scalar(const unsigned char* src, unsigned char* dest, size_t len,
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}
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i++;
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}
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// do final char; we process this separately to prevent an overflow if the final char is '='
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if (i == -1) {
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if(i == -1) {
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c = es[i];
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if (c != '\n' && c != '\r' && c != '=') {
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if(c != '\n' && c != '\r' && c != '=') {
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*p++ = c - 42;
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}
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else if (state) {
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if (c == '=') *state = 1;
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else if (c == '\r') *state = 2;
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else *state = 3;
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} else if(state) {
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if(c == '=') *state = YDEC_STATE_EQ;
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else if(c == '\r') *state = YDEC_STATE_CR;
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else *state = YDEC_STATE_NONE;
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}
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}
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#undef YDEC_CHECK_END
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*src = es;
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*dest = p;
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return 0;
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}
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return p - dest;
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void init_decode_scalar() {
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decode = decode_scalar;
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}
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}
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