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SAA: optimize seeks when used on a byte array

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In practice, we only ever use the seeking functions on byte arrays
(elem_len == 1).  Optimize for that case, to avoid a general divmod
operation.
This commit is contained in:
H. Peter Anvin 2008-06-10 09:29:20 -07:00
parent 11627049ae
commit 1cff81e356
1 changed files with 17 additions and 5 deletions
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22
saa.c
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@ -3,7 +3,8 @@
#include "saa.h"
/* Aggregate SAA components smaller than this */
#define SAA_BLKLEN 65536
#define SAA_BLKSHIFT 16
#define SAA_BLKLEN ((size_t)1 << SAA_BLKSHIFT)
struct SAA *saa_init(size_t elem_len)
{
@ -210,9 +211,14 @@ void saa_fread(struct SAA *s, size_t posn, void *data, size_t len)
return;
}
ix = posn / s->blk_len;
if (s->elem_len == 1) {
ix = posn >> SAA_BLKSHIFT;
s->rpos = posn & (SAA_BLKLEN-1);
} else {
ix = posn / s->blk_len;
s->rpos = posn % s->blk_len;
}
s->rptr = posn;
s->rpos = posn % s->blk_len;
s->rblk = &s->blk_ptrs[ix];
saa_rnbytes(s, data, len);
@ -229,9 +235,15 @@ void saa_fwrite(struct SAA *s, size_t posn, const void *data, size_t len)
return;
}
ix = posn / s->blk_len;
if (s->elem_len == 1) {
ix = posn >> SAA_BLKSHIFT;
s->wpos = posn & (SAA_BLKLEN-1);
} else {
ix = posn / s->blk_len;
s->wpos = posn % s->blk_len;
}
s->wptr = posn;
s->wpos = posn % s->blk_len;
s->wblk = &s->blk_ptrs[ix];
if (!s->wpos) {