varint: make it available outside the context of pack

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -627,6 +627,7 @@ LIB_H += tree-walk.h
 LIB_H += unpack-trees.h
 LIB_H += userdiff.h
 LIB_H += utf8.h
+LIB_H += varint.h
 LIB_H += xdiff-interface.h
 LIB_H += xdiff/xdiff.h
 
@@ -752,6 +753,7 @@ LIB_OBJS += url.o
 LIB_OBJS += usage.o
 LIB_OBJS += userdiff.o
 LIB_OBJS += utf8.o
+LIB_OBJS += varint.o
 LIB_OBJS += walker.o
 LIB_OBJS += wrapper.o
 LIB_OBJS += write_or_die.o

varint.c

@@ -0,0 +1,29 @@
+#include "varint.h"
+
+uintmax_t decode_varint(const unsigned char **bufp)
+{
+	const unsigned char *buf = *bufp;
+	unsigned char c = *buf++;
+	uintmax_t val = c & 127;
+	while (c & 128) {
+		val += 1;
+		if (!val || MSB(val, 7))
+			return 0; /* overflow */
+		c = *buf++;
+		val = (val << 7) + (c & 127);
+	}
+	*bufp = buf;
+	return val;
+}
+
+int encode_varint(uintmax_t value, unsigned char *buf)
+{
+	unsigned char varint[16];
+	unsigned pos = sizeof(varint) - 1;
+	varint[pos] = value & 127;
+	while (value >>= 7)
+		varint[--pos] = 128 | (--value & 127);
+	if (buf)
+		memcpy(buf, varint + pos, sizeof(varint) - pos);
+	return sizeof(varint) - pos;
+}

varint.h

@@ -0,0 +1,9 @@
+#ifndef VARINT_H
+#define VARINT_H
+
+#include "git-compat-util.h"
+
+extern int encode_varint(uintmax_t, unsigned char *);
+extern uintmax_t decode_varint(const unsigned char **);
+
+#endif /* VARINT_H */