rewrite code again to be faster and fix bug in previous commit (#235290)

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 44 insertions, 18 deletions

diff --git a/rpmoffset.c b/rpmoffset.c
index 10b7f4a..80ed563 100644
--- a/rpmoffset.c
+++ b/rpmoffset.c
@@ -4,38 +4,64 @@
 
 /* Wouldn't it be a lot more sane if we could just untar these things? */
 
+#ifndef _GNU_SOURCE
+# define _GNU_SOURCE
+#endif
+
+#include <stdint.h>
 #include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
+#include <string.h>
+
+#ifndef ARRAY_SIZE
+# define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
+#endif
+#ifndef BUFSIZ
+# define BUFSIZ 8192
+#endif
+
+#define MAGIC_SIZE 3
 
 int main(int argc, char *argv[])
 {
-	size_t i;
-	unsigned char p[3];
+	size_t i, read_cnt, offset, left;
+	FILE *fp = stdin;
+	char p[BUFSIZ];
+
+	const char magics[][MAGIC_SIZE] = {
+		{ '\037', '\213', '\010' },   /* gzip */
+		{ 'B', 'Z', 'h' },            /* bzip */
+	};
 
 	if (argc != 1) {
 		puts("Usage: rpmoffset < rpmfile");
 		return 1;
 	}
+	/* fp = fopen(argv[1], "r"); */
 
-	if (read(0,p,3) != 3)
-		return 2;
+	offset = left = 0;
+	while (1) {
+		read_cnt = fread(p + left, 1, sizeof(p) - left, fp);
+		if (read_cnt + left < MAGIC_SIZE)
+			break;
 
-	for (i = 0; p[2] != 0 || p[2] != 0xff; ++i) {
-		if (p[0] == '\037' && p[1] == '\213' && p[2] == '\010') {
-			printf("%zu\n", i);
-			return 0;
-
-		} else if (p[0] == 'B' && p[1] == 'Z' && p[2] == 'h') {
-			printf("%zu\n", i);
-			return 0;
+		for (i = 0; i < ARRAY_SIZE(magics); ++i) {
+			char *needle = memmem(p, sizeof(p), magics[i], MAGIC_SIZE);
+			if (needle) {
+				printf("%zu\n", offset + (needle - p));
+				return 0;
+			}
 		}
 
-		p[0] = p[1];
-		p[1] = p[2];
-		if (read(0, p+2, 1) != 1)
-			return 2;
+		offset += read_cnt;
+		if (left == 0) {
+			offset -= MAGIC_SIZE - 1;
+			left = MAGIC_SIZE - 1;
+		}
+		memmove(p, p + read_cnt - MAGIC_SIZE - 1, MAGIC_SIZE - 1);
 	}
 
+	if (ferror(stdin))
+		perror(argv[0]);
+
 	return 1;
 }