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diff: avoid repeated scanning while looking for funcname 

For each hunk, xdl_find_func searches the preimage for a function name
until the beginning of the file. If the file does not contain any
function names, this search has complexity O(n^2) in the number of
hunks n.

Instead, inline xdl_find_func() and keep track of up to which line we
have scanned already and the contents of the last funcname line that
we have found.

Noticed and a different approach proposed by Clemens Buchacher.
This alternative solution was done by René Scharfe.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
René Scharfe 2010-09-26 18:26:56 +02:00 committed by Junio C Hamano
parent ad14b450c0
commit c099789bb0
1 changed files with 14 additions and 24 deletions
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38
xdiff/xemit.c
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@ -85,27 +85,6 @@ static long def_ff(const char *rec, long len, char *buf, long sz, void *priv)
return -1;
}
static void xdl_find_func(xdfile_t *xf, long i, char *buf, long sz, long *ll,
find_func_t ff, void *ff_priv) {
/*
* Be quite stupid about this for now. Find a line in the old file
* before the start of the hunk (and context) which starts with a
* plausible character.
*/
const char *rec;
long len;
while (i-- > 0) {
len = xdl_get_rec(xf, i, &rec);
if ((*ll = ff(rec, len, buf, sz, ff_priv)) >= 0)
return;
}
*ll = 0;
}
static int xdl_emit_common(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
xdemitconf_t const *xecfg) {
xdfile_t *xdf = &xe->xdf1;
@ -127,6 +106,7 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
xdchange_t *xch, *xche;
char funcbuf[80];
long funclen = 0;
long funclineprev = -1;
find_func_t ff = xecfg->find_func ? xecfg->find_func : def_ff;
if (xecfg->flags & XDL_EMIT_COMMON)
@ -150,9 +130,19 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
*/
if (xecfg->flags & XDL_EMIT_FUNCNAMES) {
xdl_find_func(&xe->xdf1, s1, funcbuf,
sizeof(funcbuf), &funclen,
ff, xecfg->find_func_priv);
long l;
for (l = s1 - 1; l >= 0 && l > funclineprev; l--) {
const char *rec;
long reclen = xdl_get_rec(&xe->xdf1, l, &rec);
long newfunclen = ff(rec, reclen, funcbuf,
sizeof(funcbuf),
xecfg->find_func_priv);
if (newfunclen >= 0) {
funclen = newfunclen;
break;
}
}
funclineprev = s1 - 1;
}
if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
funcbuf, funclen, ecb) < 0)