X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/rsbs2/blobdiff_plain/190cff1382ffb8c929861f8c19983c778f3f0559..972ac24b5466e95d78f4af724c2f4e197f340eb5:/rsb-crc.c

diff --git a/rsb-crc.c b/rsb-crc.c
new file mode 100644
index 0000000..84b7fa2
--- /dev/null
+++ b/rsb-crc.c
@@ -0,0 +1,64 @@
+#define POLY 0x04c11db7
+
+/* Theory of operation:
+ * (arm-elf-objdump -b binary -m arm -M reg-names-raw -D RSB_S2_SINGLE.bin)
+ *
+ * 440: push  {r4, r5, r6, r7, r8, r9, r10, r11, r14}
+ * 444: mov   r11, r0
+ * 448: mov   r10, r1
+ * 44c: mov   r14, r2
+ * 450: mov   r6, #0	; 0x0
+ * 454: b     0x4a0
+ * 458: add   r3, r6, r10
+ * 45c: ldrb  r3, [r3]
+ * 460: lsl   r3, r3, #24
+ * 464: eor   r11, r11, r3
+ * 468: mov   r5, #8	; 0x8
+ * 46c: and   r3, r11, #-2147483648	; 0x80000000
+ * 470: cmp   r3, #0	; 0x0
+ * 474: beq   0x48c
+ * 478: lsl   r3, r11, #1
+ * 47c: ldr   r12, [pc, #64]	; 0x4c4
+ * 480: eor   r0, r3, r12
+ * 484: mov   r11, r0
+ * 488: b     0x490
+ * 48c: lsl   r11, r11, #1
+ * 490: sub   r5, r5, #1	; 0x1
+ * 494: cmp   r5, #0		; 0x0
+ * 498: bne   0x46c
+ * 49c: add   r6, r6, #1	; 0x1
+ * 4a0: cmp   r6, r14
+ * 4a4: blt   0x458
+ * 4a8: mov   r0, r11
+ * 4ac: pop   {r4, r5, r6, r7, r8, r9, r10, r11, r15}
+ * 4c4: DATA: 0x04c11db7
+ */
+
+unsigned int rsb_crc(unsigned int r11, unsigned char *r10, unsigned int r14) {
+	unsigned int r6 = 0;
+	unsigned int r3;
+	int r5;
+
+	while (r6 < r14) {
+		r3 = (*(r6+r10)) << 24;
+		r11 = r11 ^ r3;
+
+		r5 = 8;
+		
+		do {
+			r3 = r11 & 0x80000000;
+
+			if (r3 != 0) {
+				r3 = r11 << 1;
+				r11 = r3 ^ POLY;
+			} else {
+				r11 = r11 << 1;
+			}
+			r5--;
+		} while (r5);
+
+		r6++;
+	}
+
+	return r11;
+}