Re(-re)*fix trim_common_tail()

The tar-ball and the git archive itself is fine, but yes, the diff from 2.6.23 to 2.6.24-rc6 is bad. It's the "trim_common_tail()" optimization that has caused way too much pain. Very interesting breakage. The patch was actually "correct" in a (rather limited) technical sense, but the context at the end was missing because while the trim_common_tail() code made sure to keep enough common context to allow a valid diff to be generated, the diff machinery itself could decide that it could generate the diff differently than the "obvious" solution. Thee sad fact is that the git optimization (which is very important for "git blame", which needs no context), is only really valid for that one case where we really don't need any context. [jc: since this is shared with "git diff -U0" codepath, context recovery to the end of line needs to be done even for zero context case.] Signed-off-by: Junio C Hamano <gitster@pobox.com>

Linus Torvalds committed Dec 20, 2007 at 20:22 UTC d2f82950a9226ae1102a7a97f03440a4bf8c6c09

1 file changed +7 -4

xdiff-interface.c

+7 -4

@@ -115,17 +115,20 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b, long ctx)

115 char *bp = b->ptr + b->size;

116 long smaller = (a->size < b->size) ? a->size : b->size;

117

118 + if (ctx)

119 + return;

120 +

121 while (blk + trimmed <= smaller && !memcmp(ap - blk, bp - blk, blk)) {

122 trimmed += blk;

123 ap -= blk;

124 bp -= blk;

125 }

126

124 - while (recovered < trimmed && 0 <= ctx)

127 + while (recovered < trimmed)

128 if (ap[recovered++] == '\n')

126 - ctx--;

127 - a->size -= (trimmed - recovered);

128 - b->size -= (trimmed - recovered);

129 + break;

130 + a->size -= trimmed - recovered;

131 + b->size -= trimmed - recovered;

132 }

133

134 int xdi_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdemitconf_t const *xecfg, xdemitcb_t *xecb)