[RFC/PATCH 3/3] xdiff/xprepare: use a smaller sample size for histogram diff
- From
Tay Ray Chuan <rctay89@gmail.com>
- Date
- Jul 12, 2011, 06:10 UTC
- Message-ID
- <1310451027-15148-4-git-send-email-rctay89@gmail.com>
- In-Reply-To
- <1310451027-15148-3-git-send-email-rctay89@gmail.com>
For histogram diff, we can afford a smaller sample size and thus a poorer estimate of the number of lines, as the hash table (rhash) won't be filled up/grown. This is safe as the final count of lines (xdf.nrecs) will be updated correctly anyway by xdl_prepare_ctx().
This gives us a small boost in performance.
Signed-off-by: Tay Ray Chuan <rctay89@gmail.com> --- xdiff/xprepare.c | 17 ++++++++++++++--- xdiff/xutils.c | 8 ++------ xdiff/xutils.h | 2 +- 3 files changed, 17 insertions(+), 10 deletions(-)
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c index 7556538..dfbb0de 100644 --- a/xdiff/xprepare.c +++ b/xdiff/xprepare.c @@ -26,6 +26,8 @@ #define XDL_KPDIS_RUN 4 #define XDL_MAX_EQLIMIT 1024 #define XDL_SIMSCAN_WINDOW 100 +#define XDL_GUESS_NLINES1 256 +#define XDL_GUESS_NLINES2 20 typedef struct s_xdlclass { @@ -239,11 +241,20 @@ static void xdl_free_ctx(xdfile_t *xdf) { int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdfenv_t *xe) { - long enl1, enl2; + long enl1, enl2, sample; xdlclassifier_t cf; - enl1 = xdl_guess_lines(mf1) + 1; - enl2 = xdl_guess_lines(mf2) + 1; + /* + * For histogram diff, we can afford a smaller sample size and + * thus a poorer estimate of the number of lines, as the hash + * table (rhash) won't be filled up/grown. The number of lines + * (nrecs) will be updated correctly anyway by + * xdl_prepare_ctx(). + */ + sample = xpp->flags & XDF_HISTOGRAM_DIFF ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1; + + enl1 = xdl_guess_lines(mf1, sample) + 1; + enl2 = xdl_guess_lines(mf2, sample) + 1; if (!(xpp->flags & XDF_HISTOGRAM_DIFF) && xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0) { diff --git a/xdiff/xutils.c b/xdiff/xutils.c index ded7c32..a45e89b 100644 --- a/xdiff/xutils.c +++ b/xdiff/xutils.c @@ -24,10 +24,6 @@ -#define XDL_GUESS_NLINES 256 - - - long xdl_bogosqrt(long n) { long i; @@ -159,12 +155,12 @@ void *xdl_cha_next(chastore_t *cha) { } -long xdl_guess_lines(mmfile_t *mf) { +long xdl_guess_lines(mmfile_t *mf, long sample) { long nl = 0, size, tsize = 0; char const *data, *cur, *top; if ((cur = data = xdl_mmfile_first(mf, &size)) != NULL) { - for (top = data + size; nl < XDL_GUESS_NLINES;) { + for (top = data + size; nl < sample;) { if (cur >= top) { tsize += (long) (cur - data); if (!(cur = data = xdl_mmfile_next(mf, &size))) diff --git a/xdiff/xutils.h b/xdiff/xutils.h index 674a657..714719a 100644 --- a/xdiff/xutils.h +++ b/xdiff/xutils.h @@ -33,7 +33,7 @@ void xdl_cha_free(chastore_t *cha); void *xdl_cha_alloc(chastore_t *cha); void *xdl_cha_first(chastore_t *cha); void *xdl_cha_next(chastore_t *cha); -long xdl_guess_lines(mmfile_t *mf); +long xdl_guess_lines(mmfile_t *mf, long sample); int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags); unsigned long xdl_hash_record(char const **data, char const *top, long flags); unsigned int xdl_hashbits(unsigned int size);
-- 1.7.3.4.681.gb718e