branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
#ifndef HG_BITMANIPULATION_H
#define HG_BITMANIPULATION_H
#include <string.h>
#include "compat.h"
/* Reads a 64 bit integer from big-endian bytes. Assumes that the data is long
enough */
static inline uint64_t getbe64(const char *c)
{
const unsigned char *d = (const unsigned char *)c;
return ((((uint64_t)d[0]) << 56) | (((uint64_t)d[1]) << 48) |
(((uint64_t)d[2]) << 40) | (((uint64_t)d[3]) << 32) |
(((uint64_t)d[4]) << 24) | (((uint64_t)d[5]) << 16) |
(((uint64_t)d[6]) << 8) | (d[7]));
}
static inline uint32_t getbe32(const char *c)
{
const unsigned char *d = (const unsigned char *)c;
return ((((uint32_t)d[0]) << 24) | (((uint32_t)d[1]) << 16) |
(((uint32_t)d[2]) << 8) | (d[3]));
}
static inline int16_t getbeint16(const char *c)
{
const unsigned char *d = (const unsigned char *)c;
return ((d[0] << 8) | (d[1]));
}
static inline uint16_t getbeuint16(const char *c)
{
const unsigned char *d = (const unsigned char *)c;
return ((d[0] << 8) | (d[1]));
}
/* Writes a 64 bit integer to bytes in a big-endian format.
Assumes that the buffer is long enough */
static inline void putbe64(uint64_t x, char *c)
{
c[0] = (x >> 56) & 0xff;
c[1] = (x >> 48) & 0xff;
c[2] = (x >> 40) & 0xff;
c[3] = (x >> 32) & 0xff;
c[4] = (x >> 24) & 0xff;
c[5] = (x >> 16) & 0xff;
c[6] = (x >> 8) & 0xff;
c[7] = (x)&0xff;
}
static inline void putbe32(uint32_t x, char *c)
{
c[0] = (x >> 24) & 0xff;
c[1] = (x >> 16) & 0xff;
c[2] = (x >> 8) & 0xff;
c[3] = (x)&0xff;
}
static inline double getbefloat64(const char *c)
{
const unsigned char *d = (const unsigned char *)c;
double ret;
int i;
uint64_t t = 0;
for (i = 0; i < 8; i++) {
t = (t << 8) + d[i];
}
memcpy(&ret, &t, sizeof(t));
return ret;
}
#endif