Merge branch 'jk/pack-bitmap'

Borrow the bitmap index into packfiles from JGit to speed up
enumeration of objects involved in a commit range without having to
fully traverse the history.

* jk/pack-bitmap: (26 commits)
  ewah: unconditionally ntohll ewah data
  ewah: support platforms that require aligned reads
  read-cache: use get_be32 instead of hand-rolled ntoh_l
  block-sha1: factor out get_be and put_be wrappers
  do not discard revindex when re-preparing packfiles
  pack-bitmap: implement optional name_hash cache
  t/perf: add tests for pack bitmaps
  t: add basic bitmap functionality tests
  count-objects: recognize .bitmap in garbage-checking
  repack: consider bitmaps when performing repacks
  repack: handle optional files created by pack-objects
  repack: turn exts array into array-of-struct
  repack: stop using magic number for ARRAY_SIZE(exts)
  pack-objects: implement bitmap writing
  rev-list: add bitmap mode to speed up object lists
  pack-objects: use bitmaps when packing objects
  pack-objects: split add_object_entry
  pack-bitmap: add support for bitmap indexes
  documentation: add documentation for the bitmap format
  ewah: compressed bitmap implementation
  ...

compat/bswap.h

@@ -17,7 +17,20 @@ static inline uint32_t default_swab32(uint32_t val)
 		((val & 0x000000ff) << 24));
 }
 
+static inline uint64_t default_bswap64(uint64_t val)
+{
+	return (((val & (uint64_t)0x00000000000000ffULL) << 56) |
+		((val & (uint64_t)0x000000000000ff00ULL) << 40) |
+		((val & (uint64_t)0x0000000000ff0000ULL) << 24) |
+		((val & (uint64_t)0x00000000ff000000ULL) <<  8) |
+		((val & (uint64_t)0x000000ff00000000ULL) >>  8) |
+		((val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
+		((val & (uint64_t)0x00ff000000000000ULL) >> 40) |
+		((val & (uint64_t)0xff00000000000000ULL) >> 56));
+}
+
 #undef bswap32
+#undef bswap64
 
 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
 
@@ -32,15 +45,42 @@ static inline uint32_t git_bswap32(uint32_t x)
 	return result;
 }
 
+#define bswap64 git_bswap64
+#if defined(__x86_64__)
+static inline uint64_t git_bswap64(uint64_t x)
+{
+	uint64_t result;
+	if (__builtin_constant_p(x))
+		result = default_bswap64(x);
+	else
+		__asm__("bswap %q0" : "=r" (result) : "0" (x));
+	return result;
+}
+#else
+static inline uint64_t git_bswap64(uint64_t x)
+{
+	union { uint64_t i64; uint32_t i32[2]; } tmp, result;
+	if (__builtin_constant_p(x))
+		result.i64 = default_bswap64(x);
+	else {
+		tmp.i64 = x;
+		result.i32[0] = git_bswap32(tmp.i32[1]);
+		result.i32[1] = git_bswap32(tmp.i32[0]);
+	}
+	return result.i64;
+}
+#endif
+
 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
 
 #include <stdlib.h>
 
 #define bswap32(x) _byteswap_ulong(x)
+#define bswap64(x) _byteswap_uint64(x)
 
 #endif
 
-#ifdef bswap32
+#if defined(bswap32)
 
 #undef ntohl
 #undef htonl
@@ -48,3 +88,73 @@ static inline uint32_t git_bswap32(uint32_t x)
 #define htonl(x) bswap32(x)
 
 #endif
+
+#if defined(bswap64)
+
+#undef ntohll
+#undef htonll
+#define ntohll(x) bswap64(x)
+#define htonll(x) bswap64(x)
+
+#else
+
+#undef ntohll
+#undef htonll
+
+#if !defined(__BYTE_ORDER)
+# if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
+#  define __BYTE_ORDER BYTE_ORDER
+#  define __LITTLE_ENDIAN LITTLE_ENDIAN
+#  define __BIG_ENDIAN BIG_ENDIAN
+# endif
+#endif
+
+#if !defined(__BYTE_ORDER)
+# error "Cannot determine endianness"
+#endif
+
+#if __BYTE_ORDER == __BIG_ENDIAN
+# define ntohll(n) (n)
+# define htonll(n) (n)
+#else
+# define ntohll(n) default_bswap64(n)
+# define htonll(n) default_bswap64(n)
+#endif
+
+#endif
+
+/*
+ * Performance might be improved if the CPU architecture is OK with
+ * unaligned 32-bit loads and a fast ntohl() is available.
+ * Otherwise fall back to byte loads and shifts which is portable,
+ * and is faster on architectures with memory alignment issues.
+ */
+
+#if defined(__i386__) || defined(__x86_64__) || \
+    defined(_M_IX86) || defined(_M_X64) || \
+    defined(__ppc__) || defined(__ppc64__) || \
+    defined(__powerpc__) || defined(__powerpc64__) || \
+    defined(__s390__) || defined(__s390x__)
+
+#define get_be16(p)	ntohs(*(unsigned short *)(p))
+#define get_be32(p)	ntohl(*(unsigned int *)(p))
+#define put_be32(p, v)	do { *(unsigned int *)(p) = htonl(v); } while (0)
+
+#else
+
+#define get_be16(p)	( \
+	(*((unsigned char *)(p) + 0) << 8) | \
+	(*((unsigned char *)(p) + 1) << 0) )
+#define get_be32(p)	( \
+	(*((unsigned char *)(p) + 0) << 24) | \
+	(*((unsigned char *)(p) + 1) << 16) | \
+	(*((unsigned char *)(p) + 2) <<  8) | \
+	(*((unsigned char *)(p) + 3) <<  0) )
+#define put_be32(p, v)	do { \
+	unsigned int __v = (v); \
+	*((unsigned char *)(p) + 0) = __v >> 24; \
+	*((unsigned char *)(p) + 1) = __v >> 16; \
+	*((unsigned char *)(p) + 2) = __v >>  8; \
+	*((unsigned char *)(p) + 3) = __v >>  0; } while (0)
+
+#endif