From 4e0f09e57fe576f6280c410e99f7b13277e66fec Mon Sep 17 00:00:00 2001
From: Connor Olding <cloningdonor@gmail.com>
Date: Sun, 5 Aug 2012 19:58:43 -0700
Subject: [PATCH] offload crc table handling

---
 crc32.c | 45 ++++++++++++++-------------------------------
 crc32.h |  7 ++++---
 main.c  | 12 ++++++++----
 3 files changed, 26 insertions(+), 38 deletions(-)

diff --git a/crc32.c b/crc32.c
index 94680c4..9c05f78 100644
--- a/crc32.c
+++ b/crc32.c
@@ -5,10 +5,7 @@
  * copy of the license along with this program; see the file LICENSE.
  */
 
-#include <stdlib.h>
-
 typedef unsigned long ulong;
-
 #include "crc32.h"
 
 int crc_big_endian = 0;
@@ -17,8 +14,6 @@ ulong crc_polynomial = 0x04C11DB7;
 enum {
 	TABLE_SIZE = 0x100
 };
-static ulong crc_be_table[TABLE_SIZE]; /* big endian */
-static ulong crc_le_table[TABLE_SIZE]; /* little endian */
 
 ulong crc_reflect(ulong input)
 {
@@ -32,47 +27,35 @@ ulong crc_reflect(ulong input)
 	return reflected;
 }
 
-static void crc_fill_table(int big)
+/* TODO: test returning array */
+void crc_fill_table(ulong *table, int big, ulong polynomial)
 {
 	ulong lsb = (big) ? 1 << 31 : 1; /* least significant bit */
-	ulong poly = (big) ? crc_polynomial : crc_reflect(crc_polynomial);
-	ulong *tc = (big) ? crc_be_table : crc_le_table;
+	ulong poly = (big) ? polynomial : crc_reflect(polynomial);
 	int c, i;
 
-	for (c = 0; c < TABLE_SIZE; c++, tc++) {
-		*tc = (big) ? c << 24 : c;
+	for (c = 0; c < TABLE_SIZE; c++, table++) {
+		*table = (big) ? c << 24 : c;
 		for (i = 0; i < 8; i++) {
-			if (*tc & lsb) {
-				*tc = (big) ? *tc << 1 : *tc >> 1;
-				*tc ^= poly;
+			if (*table & lsb) {
+				*table = (big) ? *table << 1 : *table >> 1;
+				*table ^= poly;
 			} else {
-				*tc = (big) ? *tc << 1 : *tc >> 1;
+				*table = (big) ? *table << 1 : *table >> 1;
 			}
-			*tc &= 0xFFFFFFFF;
+			*table &= 0xFFFFFFFF;
 		}
 	}
 }
 
-void crc_be_cycle(ulong *remainder, char c)
+void crc_be_cycle(ulong *table, ulong *remainder, char c)
 {
-	static char filled = 0;
-	ulong byte;
-	if (!filled) {
-		crc_fill_table(1);
-		filled = 1;
-	}
-	byte = crc_be_table[((*remainder) >> 24) ^ c];
+	ulong byte = table[((*remainder) >> 24) ^ c];
 	*remainder = (((*remainder) << 8) ^ byte) & 0xFFFFFFFF;
 }
 
-void crc_le_cycle(ulong *remainder, char c)
+void crc_le_cycle(ulong *table, ulong *remainder, char c)
 {
-	static char filled = 0;
-	ulong byte;
-	if (!filled) {
-		crc_fill_table(0);
-		filled = 1;
-	}
-	byte = crc_le_table[((*remainder) ^ c) & 0xFF];
+	ulong byte = table[((*remainder) ^ c) & 0xFF];
 	*remainder = ((*remainder) >> 8) ^ byte;
 }
diff --git a/crc32.h b/crc32.h
index aa4dc99..4e43b4a 100644
--- a/crc32.h
+++ b/crc32.h
@@ -5,8 +5,9 @@
  * copy of the license along with this program; see the file LICENSE.
  */
 
-ulong crc_polynomial;
+enum { CRC_TABLE_SIZE = 0x100 };
 
-void crc_be_cycle(ulong *remainder, char c);
-void crc_le_cycle(ulong *remainder, char c);
+void crc_fill_table(ulong *table, int big, ulong polynomial);
+void crc_be_cycle(ulong *table, ulong *remainder, char c);
+void crc_le_cycle(ulong *table, ulong *remainder, char c);
 ulong crc_reflect(ulong input);
diff --git a/main.c b/main.c
index 7da9a78..264e862 100644
--- a/main.c
+++ b/main.c
@@ -35,6 +35,7 @@ static string_node *input_node = NULL;
 
 static ulong starting = 0xFFFFFFFF;
 static char big_endian = 0;
+static ulong polynomial = 0x04C11DB7;
 static char print_binary = 0;
 static char xor_output = 1;
 static char reflect_output = 0;
@@ -90,7 +91,7 @@ static void handle_flag(char flag, char *(*nextarg)())
 		break;
 	case 'p':
 		next = check_next(flag, nextarg());
-		crc_polynomial = strtoul(next, NULL, 0);
+		polynomial = strtoul(next, NULL, 0);
 		break;
 	default:
 		fprintf(stderr, "Unknown flag: -%c\n", flag);
@@ -130,9 +131,12 @@ static FILE *open_stream(char *filename)
 static ulong cycle_file(FILE *stream)
 {
 	ulong remainder = starting;
-	void (*cycle)(ulong*, char) = (big_endian) ? crc_be_cycle : crc_le_cycle;
-
+	void (*cycle)(ulong*, ulong*, char) =
+	    (big_endian) ? crc_be_cycle : crc_le_cycle;
+	ulong table[CRC_TABLE_SIZE];
 	int i, len;
+
+	crc_fill_table(table, big_endian, polynomial);
 	do {
 		len = fread(buff, 1, BUFFER_SIZE, stream);
 		if (ferror(stream)) {
@@ -141,7 +145,7 @@ static ulong cycle_file(FILE *stream)
 		}
 
 		for (i = 0; i < len; i++)
-			cycle(&remainder, buff[i]);
+			cycle(table, &remainder, buff[i]);
 	} while (!feof(stream));
 
 	if (xor_output)