Add "check_sha1_signature()" helper function

And fix up header declarations.

cache.h

@@ -82,6 +82,7 @@ extern int write_sha1_buffer(unsigned char *sha1, void *buf, unsigned int size);
 
 /* Read and unpack a sha1 file into memory, write memory to a sha1 file */
 extern void * map_sha1_file(unsigned char *sha1, unsigned long *size);
+extern void * unpack_sha1_file(void *map, unsigned long mapsize, char *type, unsigned long *size);
 extern void * read_sha1_file(unsigned char *sha1, char *type, unsigned long *size);
 extern int write_sha1_file(char *buf, unsigned len);
 extern int check_sha1_signature(unsigned char *sha1, void *buf, unsigned long size);

read-cache.c

@@ -84,6 +84,17 @@ char *sha1_file_name(unsigned char *sha1)
 	return base;
 }
 
+int check_sha1_signature(unsigned char *sha1, void *map, unsigned long size)
+{
+	unsigned char real_sha1[20];
+	SHA_CTX c;
+
+	SHA1_Init(&c);
+	SHA1_Update(&c, map, size);
+	SHA1_Final(real_sha1, &c);
+	return memcmp(sha1, real_sha1, 20) ? -1 : 0;
+}
+
 void *map_sha1_file(unsigned char *sha1, unsigned long *size)
 {
 	char *filename = sha1_file_name(sha1);