mercurial/mpatch.h

branchmap: add a cache validation cache, avoid expensive re-hash on every use

In a pathological `hg log` case, we end up executing the branchmap validity
checking twice per commit displayed. Or maybe we always do, and I just noticed
because it's really slow in this repo for some reason.

Before:
```
  Time (mean ± σ):      9.816 s ±  0.071 s    [User: 9.435 s, System: 0.392 s]

  Range (min … max):    9.709 s …  9.920 s
```

After:
```
  Time (mean ± σ):      8.671 s ±  0.078 s    [User: 8.309 s, System: 0.392 s]

  Range (min … max):    8.594 s …  8.816 s
```

Differential Revision: https://phab.mercurial-scm.org/D9023

#ifndef _HG_MPATCH_H_
#define _HG_MPATCH_H_

#define MPATCH_ERR_NO_MEM -3
#define MPATCH_ERR_CANNOT_BE_DECODED -2
#define MPATCH_ERR_INVALID_PATCH -1

struct mpatch_frag {
	int start, end, len;
	const char *data;
};

struct mpatch_flist {
	struct mpatch_frag *base, *head, *tail;
};

int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist **res);
ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l);
void mpatch_lfree(struct mpatch_flist *a);
int mpatch_apply(char *buf, const char *orig, ssize_t len,
                 struct mpatch_flist *l);
struct mpatch_flist *
mpatch_fold(void *bins, struct mpatch_flist *(*get_next_item)(void *, ssize_t),
            ssize_t start, ssize_t end);

#endif