helper: Add generic little endian CRC32 function

This generalizes the little endian CRC32 function used in the OR1K
target and moves it to a common helper, so that other places do not need
to reinvent the wheel. It is directly used in the OR1K target.

Change-Id: I0e55340281a5bfd80669bb1994f3a96fecc1248a
Signed-off-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/7415
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/helper/Makefile.am

@@ -9,6 +9,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/configuration.c \
 	%D%/log.c \
 	%D%/command.c \
+	%D%/crc32.c \
 	%D%/time_support.c \
 	%D%/replacements.c \
 	%D%/fileio.c \
@@ -24,6 +25,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/types.h \
 	%D%/log.h \
 	%D%/command.h \
+	%D%/crc32.h \
 	%D%/time_support.h \
 	%D%/replacements.h \
 	%D%/fileio.h \

src/helper/crc32.c

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/***************************************************************************
+ *   Copyright (C) 2013-2014 by Franck Jullien                             *
+ *   elec4fun@gmail.com                                                    *
+ *                                                                         *
+ *   Copyright (C) 2022 Otto-von-Guericke-Universität Magdeburg            *
+ *   marian.buschsieweke@ovgu.de                                           *
+ ***************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "crc32.h"
+#include <stdint.h>
+#include <stddef.h>
+
+static uint32_t crc_le_step(uint32_t poly, uint32_t crc, uint32_t data_in,
+		unsigned int data_bits)
+{
+	for (unsigned int i = 0; i < data_bits; i++) {
+		uint32_t d, c;
+		d = ((data_in >> i) & 0x1) ? 0xffffffff : 0;
+		c = (crc & 0x1) ? 0xffffffff : 0;
+		crc = crc >> 1;
+		crc = crc ^ ((d ^ c) & poly);
+	}
+
+	return crc;
+}
+
+uint32_t crc32_le(uint32_t poly, uint32_t seed, const void *_data,
+		size_t data_len)
+{
+	if (((uintptr_t)_data & 0x3) || (data_len & 0x3)) {
+		/* data is unaligned, processing data one byte at a time */
+		const uint8_t *data = _data;
+		for (size_t i = 0; i < data_len; i++)
+			seed = crc_le_step(poly, seed, data[i], 8);
+	} else {
+		/* data is aligned, processing 32 bit at a time */
+		data_len >>= 2;
+		const uint32_t *data = _data;
+		for (size_t i = 0; i < data_len; i++)
+			seed = crc_le_step(poly, seed, data[i], 32);
+	}
+
+	return seed;
+}

src/helper/crc32.h

@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/***************************************************************************
+ *   Copyright (C) 2022 Otto-von-Guericke-Universität Magdeburg            *
+ *   marian.buschsieweke@ovgu.de                                           *
+ ***************************************************************************/
+
+#ifndef OPENOCD_HELPER_CRC32_H
+#define OPENOCD_HELPER_CRC32_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+/** @file
+ * A generic CRC32 implementation
+ */
+
+/**
+ * CRC32 polynomial commonly used for little endian CRC32
+ */
+#define CRC32_POLY_LE	0xedb88320
+
+/**
+ * Calculate the CRC32 value of the given data
+ * @param	poly		The polynomial of the CRC
+ * @param	seed		The seed to use (mostly either `0` or `0xffffffff`)
+ * @param	data		The data to calculate the CRC32 of
+ * @param	data_len	The length of the data in @p data in bytes
+ * @return	The CRC value of the first @p data_len bytes at @p data
+ * @note	This function can be used to incrementally compute the CRC one
+ *			chunk of data at a time by using the CRC32 of the previous chunk
+ *			as @p seed for the next chunk.
+ */
+uint32_t crc32_le(uint32_t poly, uint32_t seed, const void *data,
+		size_t data_len);
+
+#endif /* OPENOCD_HELPER_CRC32_H */

src/target/openrisc/or1k_du_adv.c

@@ -22,8 +22,9 @@
 #include "or1k_du.h"
 #include "jsp_server.h"
 
-#include <target/target.h>
+#include <helper/crc32.h>
 #include <jtag/jtag.h>
+#include <target/target.h>
 
 #define JSP_BANNER "\n\r" \
 		   "******************************\n\r" \
@@ -67,13 +68,6 @@
 #define DBG_CPU_CR_STALL		0x01
 #define DBG_CPU_CR_RESET		0x02
 
-/* Polynomial for the CRC calculation
- * Yes, it's backwards.  Yes, this is on purpose.
- * The hardware is designed this way to save on logic and routing,
- * and it's really all the same to us here.
- */
-#define ADBG_CRC_POLY			0xedb88320
-
 /* These are for the internal registers in the Wishbone module
  * The first is the length of the index register,
  * the indexes of the various registers are defined after that.
@@ -133,20 +127,6 @@ static struct or1k_du or1k_du_adv;
 
 static const char * const chain_name[] = {"WISHBONE", "CPU0", "CPU1", "JSP"};
 
-static uint32_t adbg_compute_crc(uint32_t crc, uint32_t data_in,
-				 int length_bits)
-{
-	for (int i = 0; i < length_bits; i++) {
-		uint32_t d, c;
-		d = ((data_in >> i) & 0x1) ? 0xffffffff : 0;
-		c = (crc & 0x1) ? 0xffffffff : 0;
-		crc = crc >> 1;
-		crc = crc ^ ((d ^ c) & ADBG_CRC_POLY);
-	}
-
-	return crc;
-}
-
 static int find_status_bit(void *_buf, int len)
 {
 	int i = 0;
@@ -522,9 +502,8 @@ retry_read_full:
 	memcpy(data, in_buffer, total_size_bytes);
 	memcpy(&crc_read, &in_buffer[total_size_bytes], 4);
 
-	uint32_t crc_calc = 0xffffffff;
-	for (int i = 0; i < total_size_bytes; i++)
-		crc_calc = adbg_compute_crc(crc_calc, data[i], 8);
+	uint32_t crc_calc = crc32_le(CRC32_POLY_LE, 0xffffffff, data,
+			total_size_bytes);
 
 	if (crc_calc != crc_read) {
 		LOG_WARNING("CRC ERROR! Computed 0x%08" PRIx32 ", read CRC 0x%08" PRIx32, crc_calc, crc_read);
@@ -650,9 +629,8 @@ retry_full_write:
 	field[0].out_value = &value;
 	field[0].in_value = NULL;
 
-	uint32_t crc_calc = 0xffffffff;
-	for (int i = 0; i < (count * size); i++)
-		crc_calc = adbg_compute_crc(crc_calc, data[i], 8);
+	uint32_t crc_calc = crc32_le(CRC32_POLY_LE, 0xffffffff, data,
+			count * size);
 
 	field[1].num_bits = count * size * 8;
 	field[1].out_value = data;