From: Joshua Wise <joshua@rebirth.joshuawise.com>
Date: Mon, 15 Dec 2008 00:25:18 +0000 (-0500)
Subject: Modify crc32 users to behave better when crcing multiple things into one CRC.
X-Git-Url: http://git.joshuawise.com/netwatch.git/commitdiff_plain/f2da68c5992fe2c29cced7e51709d0a45e0bb3b4?hp=1deef7f33c284af59d562e7b50812f9649e94d0b

Modify crc32 users to behave better when crcing multiple things into one CRC.
---

diff --git a/include/crc32.h b/include/crc32.h
index f7d568a..a384bcc 100644
--- a/include/crc32.h
+++ b/include/crc32.h
@@ -3,7 +3,7 @@
 
 #include <stdint.h>
 
-extern uint32_t crc32(unsigned char *buf, int len);
+extern uint32_t crc32(unsigned char *buf, int len, uint32_t crc0);
 extern void crc32_init();
 
 #endif
diff --git a/lib/crc32.c b/lib/crc32.c
index fd7bd49..43f9d7a 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -5,15 +5,15 @@
 
 uint32_t crc32_table[256];
 
-uint32_t crc32(uint8_t *buf, int len)
+uint32_t crc32(uint8_t *buf, int len, uint32_t crc0)
 {
 	uint8_t *p;
 	uint32_t crc;
 
-	crc = 0xffffffff;       /* preload shift register, per CRC-32 spec */
+	crc = crc0;
 	for (p = buf; len > 0; ++p, --len)
 		crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
-	return ~crc;	    /* transmit complement, per CRC-32 spec */
+	return crc;
 }
 
 /*
diff --git a/video/generic.c b/video/generic.c
index 8c6866d..95f564f 100644
--- a/video/generic.c
+++ b/video/generic.c
@@ -17,7 +17,7 @@ uint32_t checksum_rect_generic32(int x, int y, int width, int height) {
         for (i = 0; i < height; i++) {
                 lineaddr = fb->fbaddr + (i + y) * scanline + (4 * x);
 
-                sum ^= crc32(lineaddr, width * 4);
+                sum = crc32(lineaddr, width * 4, sum);
         }
 
         return sum;
diff --git a/video/text.c b/video/text.c
index 25fe245..7fe30c9 100644
--- a/video/text.c
+++ b/video/text.c
@@ -91,7 +91,7 @@ uint32_t text_checksum(int x, int y, int w, int h)
 		cx = x;
 		texty = cy / 14;
 		textx = cx / 9;
-		cksm ^= crc32(video + texty * 160 + textx * 2, (w / 9 + 1) * 2);	/* Err on the side of 'too many'. */
+		cksm = crc32(video + texty * 160 + textx * 2, (w / 9) * 2 + 2, cksm);	/* Err on the side of 'too many'. */
 	}
 	
 	smram_restore_state(old_state);