minor optimizations to FLAC__bitbuffer_read_rice_signed_block()
authorJosh Coalson <jcoalson@users.sourceforce.net>
Sat, 17 Mar 2007 05:21:36 +0000 (05:21 +0000)
committerJosh Coalson <jcoalson@users.sourceforce.net>
Sat, 17 Mar 2007 05:21:36 +0000 (05:21 +0000)
src/libFLAC/bitreader.c

index 4f3874f..be09574 100644 (file)
@@ -131,6 +131,7 @@ static const unsigned char byte_to_unary_table[] = {
 #define FLaC__INLINE
 #endif
 
+/* WATCHOUT: assembly routines rely on the order in which these fields are declared */
 struct FLAC__BitReader {
        /* any partially-consumed word at the head will stay right-justified as bits are consumed from the left */
        /* any incomplete word at the tail will be left-justified, and bytes from the read callback are added on the right */
@@ -138,7 +139,8 @@ struct FLAC__BitReader {
        unsigned capacity; /* in words */
        unsigned words; /* # of completed words in buffer */
        unsigned bytes; /* # of bytes in incomplete word at buffer[words] */
-       unsigned consumed_words, consumed_bits; /* #words+(#bits of head word) already consumed from the front of buffer */
+       unsigned consumed_words; /* #words ... */
+       unsigned consumed_bits; /* ... + (#bits of head word) already consumed from the front of buffer */
        unsigned read_crc16; /* the running frame CRC */
        unsigned crc16_align; /* the number of bits in the current consumed word that should not be CRC'd */
        FLAC__BitReaderReadCallback read_callback;
@@ -201,7 +203,8 @@ static FLaC__INLINE void crc16_update_word_(FLAC__BitReader *br, brword word)
        br->crc16_align = 0;
 }
 
-static FLAC__bool bitreader_read_from_client_(FLAC__BitReader *br)
+/* would be static except it needs to be called by asm routines */
+FLAC__bool bitreader_read_from_client_(FLAC__BitReader *br)
 {
        unsigned start, end;
        size_t bytes;
@@ -827,7 +830,7 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
        /* WATCHOUT: code does not work with <32bit words; we can make things much faster with this assertion */
        FLAC__ASSERT(FLAC__BITS_PER_WORD >= 32);
        FLAC__ASSERT(parameter < 32);
-       /* the above two asserts also guarantee that the binary part never straddles more that 2 words, so we don't have to loop to read it */
+       /* the above two asserts also guarantee that the binary part never straddles more than 2 words, so we don't have to loop to read it */
 
        if(nvals == 0)
                return true;
@@ -849,9 +852,9 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
                                        i = ALIGNED_UNARY_BITS(b);
 #endif
                                        uval += i;
-                                       bits = parameter;
-                                       i++;
                                        cbits += i;
+                                       bits = parameter;
+                                       cbits++; /* skip over stop bit */
                                        if(cbits == FLAC__BITS_PER_WORD) {
                                                crc16_update_word_(br, br->buffer[cwords]);
                                                cwords++;
@@ -876,7 +879,7 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
                         */
                        if(br->bytes) {
                                const unsigned end = br->bytes * 8;
-                               brword b = (br->buffer[cwords] & (FLAC__WORD_ALL_ONES << (FLAC__BITS_PER_WORD-end))) << cbits;
+                               brword b = (br->buffer[cwords] & ~(FLAC__WORD_ALL_ONES >> end)) << cbits;
                                if(b) {
 #if 0 /* too slow, but this is the idea: */
                                        for(i = 0; !(b & FLAC__WORD_TOP_BIT_ONE); i++)
@@ -885,9 +888,9 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
                                        i = ALIGNED_UNARY_BITS(b);
 #endif
                                        uval += i;
-                                       bits = parameter;
-                                       i++;
                                        cbits += i;
+                                       bits = parameter;
+                                       cbits++; /* skip over stop bit */
                                        FLAC__ASSERT(cbits < FLAC__BITS_PER_WORD);
                                        goto break1;
                                }