From 75f1908690baa876eaf08db98f53dfd328762fc5 Mon Sep 17 00:00:00 2001
From: Dietrich Epp <depp@zdome.net>
Date: Sun, 10 Apr 2022 03:37:14 -0400
Subject: [PATCH] Add CRC-32 function

---
 lib/BUILD.bazel  | 14 ++++++++++++++
 lib/crc32.c      | 40 ++++++++++++++++++++++++++++++++++++++++
 lib/crc32.h      |  9 +++++++++
 lib/crc32_test.c | 22 ++++++++++++++++++++++
 4 files changed, 85 insertions(+)
 create mode 100644 lib/crc32.c
 create mode 100644 lib/crc32.h
 create mode 100644 lib/crc32_test.c

diff --git a/lib/BUILD.bazel b/lib/BUILD.bazel
index 09df080..4c48ef4 100644
--- a/lib/BUILD.bazel
+++ b/lib/BUILD.bazel
@@ -4,10 +4,12 @@ load("//bazel:copts.bzl", "COPTS")
 cc_library(
     name = "lib",
     srcs = [
+        "crc32.c",
         "toolbox.c",
         "util.c",
     ],
     hdrs = [
+        "crc32.h",
         "defs.h",
         "endian.h",
         "util.h",
@@ -44,3 +46,15 @@ cc_test(
         ":test",
     ],
 )
+
+cc_test(
+    name = "crc32_test",
+    size = "small",
+    srcs = [
+        "crc32_test.c",
+    ],
+    copts = COPTS,
+    deps = [
+        ":lib",
+    ],
+)
diff --git a/lib/crc32.c b/lib/crc32.c
new file mode 100644
index 0000000..75f5742
--- /dev/null
+++ b/lib/crc32.c
@@ -0,0 +1,40 @@
+#include "lib/crc32.h"
+
+static int gCRCInitted;
+static UInt32 gCRCTable[256];
+
+static void CRC32Init(void)
+{
+	int i, j;
+	UInt32 v, u;
+
+	for (i = 0; i < 256; i++) {
+		v = i;
+		for (j = 0; j < 8; j++) {
+			u = v;
+			v >>= 1;
+			if (u & 1) {
+				v ^= 0xedb88320;
+			}
+		}
+		gCRCTable[i] = v;
+	}
+	gCRCInitted = 1;
+}
+
+UInt32 CRC32Update(UInt32 crc, const void *ptr, Size size)
+{
+	const UInt8 *p, *e;
+
+	if (!gCRCInitted) {
+		CRC32Init();
+	}
+
+	crc = ~crc;
+	p = ptr;
+	e = p + size;
+	while (p < e) {
+		crc = (crc >> 8) ^ gCRCTable[(crc & 0xff) ^ *p++];
+	}
+	return ~crc;
+}
diff --git a/lib/crc32.h b/lib/crc32.h
new file mode 100644
index 0000000..803c539
--- /dev/null
+++ b/lib/crc32.h
@@ -0,0 +1,9 @@
+#ifndef CRC32_H
+#define CRC32_H
+
+#include "lib/defs.h"
+
+/* Incrementally calculate a CRC32. This is the same CRC32 used by Gzip. */
+UInt32 CRC32Update(UInt32 crc, const void *ptr, Size size);
+
+#endif
diff --git a/lib/crc32_test.c b/lib/crc32_test.c
new file mode 100644
index 0000000..2cd3000
--- /dev/null
+++ b/lib/crc32_test.c
@@ -0,0 +1,22 @@
+#include "lib/crc32.h"
+
+#include <stdio.h>
+
+static const char kTest[9] = {'1', '2', '3', '4', '5', '6', '7', '8', '9'};
+
+int main(int argc, char **argv)
+{
+	UInt32 expect;
+	UInt32 val;
+
+	(void)argc;
+	(void)argv;
+
+	expect = 0xcbf43926;
+	val = CRC32Update(0, kTest, sizeof(kTest));
+	if (val != expect) {
+		fprintf(stderr, "Error: CRC = 0x%08x, expect 0x%08x\n", val, expect);
+		return 1;
+	}
+	return 0;
+}