On Thu, 17 Nov 2016 18:16:40 +0100, Mads Kiilerich wrote:
> # HG changeset patch
> # User Mads Kiilerich <mad...@unity3d.com>
> # Date 1479322051 -3600
> # Wed Nov 16 19:47:31 2016 +0100
> # Node ID 851a14d5b80639efe61bd01ad215479c99106b40
> # Parent 7f39bccc1c96bffc83f3c6e774da57ecd38982a7
> bdiff: early pruning of common suffix before doing expensive computations
>
> Similar to the previous change, but trimming trailing lines.
>
> On mozilla-unified:
> perfbdiff -m 3041e4d59df2
> ! wall 0.024618 comb 0.020000 user 0.020000 sys 0.000000 (best of 116) to
> ! wall 0.008259 comb 0.010000 user 0.010000 sys 0.000000 (best of 356) to
> perfbdiff 0e9928989e9c --alldata --count 10
> ! wall 0.579235 comb 0.580000 user 0.580000 sys 0.000000 (best of 18)
> ! wall 0.469869 comb 0.460000 user 0.460000 sys 0.000000 (best of 22)
>
> diff --git a/mercurial/bdiff_module.c b/mercurial/bdiff_module.c
> --- a/mercurial/bdiff_module.c
> +++ b/mercurial/bdiff_module.c
> @@ -66,7 +66,7 @@ static PyObject *bdiff(PyObject *self, P
> struct bdiff_line *al, *bl;
> struct bdiff_hunk l, *h;
> int an, bn, count;
> - Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
> + Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lcommonend = 0, lmax;
> PyThreadState *_save;
>
> l.next = NULL;
> @@ -88,9 +88,16 @@ static PyObject *bdiff(PyObject *self, P
> if (*ia == '\n')
> lcommon = li + 1;
> /* we can almost add: if (li == lmax) lcommon = li; */
> + lmax -= lcommon;
> + for (li = 0, ia = sa + la - 1, ib = sb + lb - 1;
> + li <= lmax && *ia == *ib;
> + ++li, --ia, --ib)
> + if (*ia == '\n')
> + lcommonend = li;
Perhaps this could read one byte before the sa and sb. For bdiff('', ''),
li == lmax == 0 but ia == sa[-1].
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