crc sync module.

ccan/crcsync/_info.c

@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <string.h>
+#include "config.h"
+
+/**
+ * crcsync - routines to use crc for an rsync-like protocol.
+ *
+ * This is a complete library for synchronization using a variant of the
+ * rsync protocol.
+ *
+ * Example:
+ *	// Calculate checksums of file (3-arg mode)
+ *	// Or print differences between file and checksums (4+ arg mode)
+ *	#include <ccan/crcsync/crcsync.h>
+ *	#include <ccan/grab_file/grab_file.h>
+ *	#include <stdio.h>
+ *	#include <stdlib.h>
+ *	#include <err.h>
+ *	
+ *	static void print_result(long result)
+ *	{
+ *		if (result < 0)
+ *			printf("MATCHED CRC %lu\n", -result - 1);
+ *		else if (result > 0)
+ *			printf("%lu literal bytes\n", result);
+ *	}
+ *	
+ *	int main(int argc, char *argv[])
+ *	{
+ *		size_t len, used, blocksize;
+ *		char *file;
+ *		struct crc_context *ctx;
+ *		uint32_t *crcs;
+ *		long res, i;
+ *	
+ *		if (argc < 3 || (blocksize = atoi(argv[1])) == 0)
+ *			errx(1, "Usage: %s <blocksize> <file> <crc>...\n"
+ *			     "OR: %s <blocksize> <file>", argv[0], argv[0]);
+ *	
+ *		file = grab_file(NULL, argv[2], &len);
+ *		if (!file)
+ *			err(1, "Opening file %s", argv[2]);
+ *	
+ *		if (argc == 3) {
+ *			// Short form prints CRCs of file for use in long form.
+ *			used = (len + blocksize - 1) / blocksize;
+ *			crcs = malloc(used * sizeof(uint32_t));
+ *			crc_of_blocks(file, len, blocksize, 32, crcs);
+ *			for (i = 0; i < used; i++)
+ *				printf("%i ", crcs[i]);
+ *			printf("\n");
+ *			return 0;
+ *		}
+ *	
+ *		crcs = malloc((argc - 3) * sizeof(uint32_t));
+ *		for (i = 0; i < argc-3; i++)
+ *			crcs[i] = atoi(argv[3+i]);
+ *	
+ *		ctx = crc_context_new(blocksize, 32, crcs, argc-3);
+ *		for (used = 0; used < len; ) {
+ *			used += crc_read_block(ctx, &res, file+used, len-used);
+ *			print_result(res);
+ *		}
+ *		while ((res = crc_read_flush(ctx)) != 0)
+ *			print_result(res);
+ *	
+ *		return 0;
+ *	}
+ *
+ * Licence: LGPL (v2 or any later version)
+ */
+int main(int argc, char *argv[])
+{
+	if (argc != 2)
+		return 1;
+
+	if (strcmp(argv[1], "depends") == 0) {
+		printf("ccan/crc\n");
+		return 0;
+	}
+
+	return 1;
+}

ccan/crcsync/crcsync.c

@@ -0,0 +1,276 @@
+#include "crcsync.h"
+#include <ccan/crc/crc.h>
+#include <string.h>
+#include <assert.h>
+
+void crc_of_blocks(const void *data, size_t len, unsigned int block_size,
+		   unsigned int crcbits, uint32_t crc[])
+{
+	unsigned int i;
+	const uint8_t *buf = data;
+	uint32_t crcmask = crcbits < 32 ? (1 << crcbits) - 1 : 0xFFFFFFFF;
+
+	for (i = 0; len >= block_size; i++) {
+		crc[i] = (crc32c(0, buf, block_size) & crcmask);
+		buf += block_size;
+		len -= block_size;
+	}
+	if (len)
+		crc[i] = (crc32c(0, buf, len) & crcmask);
+}
+
+struct crc_context {
+	size_t block_size;
+	uint32_t crcmask;
+
+	/* Saved old buffer bytes (block_size bytes). */
+	void *buffer;
+	size_t buffer_start, buffer_end;
+
+	/* Progress so far. */
+	uint32_t running_crc;
+	size_t literal_bytes;
+	size_t total_bytes;
+	int have_match;
+
+	/* Uncrc tab. */
+	uint32_t uncrc_tab[256];
+
+	unsigned int num_crcs;
+	uint32_t crc[];
+};
+
+/* Calculate the how the crc changes when we take a give char out of the
+ * crc'd area. */
+static void init_uncrc_tab(uint32_t uncrc_tab[], unsigned int wsize)
+{
+	unsigned int i;
+	uint32_t part_crc;
+	uint8_t buffer[wsize];
+
+	/* Calculate crc(buffer+1, wsize-1) once, since it doesn't change. */
+	memset(buffer, 0, wsize);
+	part_crc = crc32c(0, buffer+1, wsize-1);
+
+	for (i = 0; i < 256; i++) {
+		buffer[0] = i;
+		uncrc_tab[i] = (crc32c(0, buffer, wsize) ^ part_crc);
+	}
+}
+
+struct crc_context *crc_context_new(size_t block_size, unsigned crcbits,
+				    const uint32_t crc[], unsigned num_crcs)
+{
+	struct crc_context *ctx;
+
+	ctx = malloc(sizeof(*ctx) + sizeof(crc[0])*num_crcs);
+	if (ctx) {
+		ctx->block_size = block_size;
+		/* Technically, 1 << 32 is undefined. */
+		if (crcbits >= 32)
+			ctx->crcmask = 0xFFFFFFFF;
+		else
+			ctx->crcmask = (1 << crcbits)-1;
+		ctx->num_crcs = num_crcs;
+		memcpy(ctx->crc, crc, sizeof(crc[0])*num_crcs);
+		ctx->buffer_end = 0;
+		ctx->buffer_start = 0;
+		ctx->running_crc = 0;
+		ctx->literal_bytes = 0;
+		ctx->total_bytes = 0;
+		ctx->have_match = -1;
+		init_uncrc_tab(ctx->uncrc_tab, block_size);
+		ctx->buffer = malloc(block_size);
+		if (!ctx->buffer) {
+			free(ctx);
+			ctx = NULL;
+		}
+	}
+	return ctx;
+}
+
+/* Return -1 or index into matching crc. */
+static int crc_matches(const struct crc_context *ctx)
+{
+	unsigned int i;
+
+	if (ctx->literal_bytes < ctx->block_size)
+		return -1;
+
+	for (i = 0; i < ctx->num_crcs; i++)
+		if ((ctx->running_crc & ctx->crcmask) == ctx->crc[i])
+			return i;
+	return -1;
+}
+
+static uint32_t crc_add_byte(uint32_t crc, uint8_t newbyte)
+{
+	return crc32c(crc, &newbyte, 1);
+}
+
+static uint32_t crc_remove_byte(uint32_t crc, uint8_t oldbyte,
+				const uint32_t uncrc_tab[])
+{
+	return crc ^ uncrc_tab[oldbyte];
+}
+
+static uint32_t crc_roll(uint32_t crc, uint8_t oldbyte, uint8_t newbyte,
+			 const uint32_t uncrc_tab[])
+{
+	return crc_add_byte(crc_remove_byte(crc, oldbyte, uncrc_tab), newbyte);
+}
+
+static size_t buffer_size(const struct crc_context *ctx)
+{
+	return ctx->buffer_end - ctx->buffer_start;
+}
+
+size_t crc_read_block(struct crc_context *ctx, long *result,
+		      const void *buf, size_t buflen)
+{
+	size_t consumed = 0, len;
+	int crcmatch = -1;
+	const uint8_t *old, *p = buf;
+
+	/* Simple optimization, if we found a match last time. */
+	if (ctx->have_match >= 0) {
+		crcmatch = ctx->have_match;
+		goto have_match;
+	}
+
+	if (buffer_size(ctx) >= ctx->block_size)
+		old = ctx->buffer + ctx->buffer_start;
+	else
+		old = NULL;
+
+	while (!old || (crcmatch = crc_matches(ctx)) < 0) {
+		if (consumed == buflen)
+			break;
+
+		/* Update crc. */
+		if (old) {
+			ctx->running_crc = crc_roll(ctx->running_crc,
+						    *old, *p,
+						    ctx->uncrc_tab);
+			old++;
+			if (old == ctx->buffer + ctx->buffer_end)
+				old = buf;
+		} else {
+			ctx->running_crc = crc_add_byte(ctx->running_crc, *p);
+			if (p == (uint8_t *)buf + ctx->block_size - 1)
+				old = buf;
+		}
+
+		ctx->literal_bytes++;
+		ctx->total_bytes++;
+		consumed++;
+		p++;
+	}
+
+	/* Make sure we have a copy of the last block_size bytes.
+	 * First, copy down the old data.  */
+	if (buffer_size(ctx)) {
+		memmove(ctx->buffer, ctx->buffer + ctx->buffer_start,
+			buffer_size(ctx));
+		ctx->buffer_end -= ctx->buffer_start;
+		ctx->buffer_start = 0;
+	}
+
+	if (crcmatch >= 0) {
+		/* We have a match! */
+		if (ctx->literal_bytes > ctx->block_size) {
+			/* Output literal first. */
+			*result = ctx->literal_bytes - ctx->block_size;
+			ctx->literal_bytes = ctx->block_size;
+			/* Remember for next time! */
+			ctx->have_match = crcmatch;
+		} else {
+		have_match:
+			*result = -crcmatch-1;
+			ctx->literal_bytes -= ctx->block_size;
+			assert(ctx->literal_bytes == 0);
+			ctx->have_match = -1;
+			ctx->running_crc = 0;
+		}
+	} else {
+		/* Output literal if it's more than 1 block ago. */
+		if (ctx->literal_bytes > ctx->block_size) {
+			*result = ctx->literal_bytes - ctx->block_size;
+			ctx->literal_bytes = ctx->block_size;
+		} else
+			*result = 0;
+
+		/* Now save any literal bytes we'll need in future. */
+		len = ctx->literal_bytes - buffer_size(ctx);
+		memcpy(ctx->buffer + ctx->buffer_end, buf, len);
+		ctx->buffer_end += len;
+		assert(buffer_size(ctx) <= ctx->block_size);
+	}
+	return consumed;
+}
+
+/* We could try many techniques to match the final block.  We can
+ * simply try to checksum whatever's left at the end and see if it
+ * matches the final block checksum.  This works for the exact-match
+ * case.
+ *
+ * We can do slightly better than this: if we try to match the checksum
+ * on every block (starting with block_size 1) from where we end to EOF,
+ * we can capture the "data appended" case as well.
+ */
+static size_t final_block_match(struct crc_context *ctx)
+{
+	size_t size;
+	uint32_t crc;
+
+	if (ctx->num_crcs == 0)
+		return 0;
+
+	crc = 0;
+	for (size = 0; size < buffer_size(ctx); size++) {
+		const uint8_t *p = ctx->buffer;
+		crc = crc_add_byte(crc, p[ctx->buffer_start+size]);
+		if ((crc & ctx->crcmask) == ctx->crc[ctx->num_crcs-1])
+			return size+1;
+	}
+	return 0;
+}
+
+long crc_read_flush(struct crc_context *ctx)
+{
+	long ret;
+
+	/* In case we ended on a whole block match. */
+	if (ctx->have_match == -1) {
+		size_t final;
+
+		final = final_block_match(ctx);
+		if (!final) {
+			/* This is how many bytes we're about to consume. */
+			ret = buffer_size(ctx);
+			ctx->buffer_start += ret;
+			ctx->literal_bytes -= ret;
+
+			return ret;
+		}
+		ctx->buffer_start += final;
+		ctx->literal_bytes -= final;
+		ctx->have_match = ctx->num_crcs-1;
+	}
+
+	/* It might be a partial block match, so no assert */
+	ctx->literal_bytes = 0;
+	ret = -ctx->have_match-1;
+	ctx->have_match = -1;
+	return ret;
+}
+
+/**
+ * crc_context_free - free a context returned from crc_context_new.
+ * @ctx: the context returned from crc_context_new, or NULL.
+ */
+void crc_context_free(struct crc_context *ctx)
+{
+	free(ctx->buffer);
+	free(ctx);
+}

ccan/crcsync/crcsync.h

@@ -0,0 +1,66 @@
+#ifndef CCAN_CRCSYNC_H
+#define CCAN_CRCSYNC_H
+#include <stdint.h>
+#include <stddef.h>
+
+/**
+ * crc_of_blocks - calculate the crc of the blocks.
+ * @data: pointer to the buffer to CRC
+ * @len: length of the buffer
+ * @blocksize: CRC of each block (final block may be shorter)
+ * @crcbits: the number of bits of crc you want (currently 32 maximum)
+ * @crc: the crcs (array will have (len + blocksize-1)/blocksize entries).
+ *
+ * Calculates the CRC of each block, and output the lower @crcbits to
+ * @crc array.
+ */
+void crc_of_blocks(const void *data, size_t len, unsigned int blocksize,
+		   unsigned int crcbits, uint32_t crc[]);
+
+/**
+ * crc_context_new - allocate and initialize state for crc_find_block
+ * @blocksize: the sie of each block
+ * @crcbits: the bits valid in the CRCs (<= 32)
+ * @crc: array of block crcs
+ * @num_crcs: number of block crcs
+ *
+ * Returns an allocated pointer to the structure for crc_find_block,
+ * or NULL.  Makes a copy of @crc and @num_crcs.
+ */
+struct crc_context *crc_context_new(size_t blocksize, unsigned crcbits,
+				    const uint32_t crc[], unsigned num_crcs);
+
+/**
+ * crc_read_block - search for block matches in the buffer.
+ * @ctx: struct crc_context from crc_context_new.
+ * @result: unmatched bytecount, or crc which matched.
+ * @buf: pointer to bytes
+ * @buflen: length of buffer
+ *
+ * Returns the number of bytes of the buffer which have been digested,
+ * and sets @result either to a negagive number (== -crc_number - 1)
+ * to show that a block matched a crc, or zero or more to represent a
+ * length of unmatched data.
+ *
+ * Note that multiple lengths of unmatched data might be returned in a row:
+ * you'll probably want to merge them yourself.
+ */
+size_t crc_read_block(struct crc_context *ctx, long *result,
+		      const void *buf, size_t buflen);
+
+/**
+ * crc_read_flush - flush any remaining data from crc_read_block.
+ * @ctx: the context passed to crc_read_block.
+ *
+ * Matches the final data.  This can be used to create a boundary, or
+ * simply flush the final data.  Keep calling it until it returns 0.
+ */
+long crc_read_flush(struct crc_context *ctx);
+
+/**
+ * crc_context_free - free a context returned from crc_context_new.
+ * @ctx: the context returned from crc_context_new, or NULL.
+ */
+void crc_context_free(struct crc_context *ctx);
+
+#endif /* CCAN_CRCSYNC_H */

ccan/crcsync/test/api.c

@@ -0,0 +1,263 @@
+#include "crcsync/crcsync.h"
+#include "crcsync/crcsync.c"
+#include "tap/tap.h"
+#include <stdlib.h>
+#include <stdbool.h>
+
+/* FIXME: ccanize. */
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+struct result {
+	enum {
+		LITERAL, BLOCK
+	} type;
+	/* Block number, or length of literal. */
+	size_t val;
+};
+
+static inline size_t num_blocks(size_t len, size_t block_size)
+{
+	return (len + block_size - 1) / block_size;
+}
+
+static void check_finalized_result(size_t curr_literal,
+				   const struct result results[],
+				   size_t num_results,
+				   size_t *curr_result)
+{
+	if (curr_literal == 0)
+		return;
+	ok1(*curr_result < num_results);
+	ok1(results[*curr_result].type == LITERAL);
+	ok1(results[*curr_result].val == curr_literal);
+	(*curr_result)++;
+}
+
+static void check_result(long result,
+			 size_t *curr_literal,
+			 const struct result results[], size_t num_results,
+			 size_t *curr_result)
+{
+	/* We append multiple literals into one. */
+	if (result >= 0) {
+		*curr_literal += result;
+		return;
+	}
+
+	/* Check outstanding literals. */
+	if (*curr_literal) {
+		check_finalized_result(*curr_literal, results, num_results,
+				       curr_result);
+		*curr_literal = 0;
+	}
+
+	ok1(*curr_result < num_results);
+	ok1(results[*curr_result].type == BLOCK);
+	ok1(results[*curr_result].val == -result - 1);
+	(*curr_result)++;
+}
+
+/* Start with buffer1 and sync to buffer2. */
+static void test_sync(const char *buffer1, size_t len1,
+		      const char *buffer2, size_t len2,
+		      size_t block_size,
+		      const struct result results[], size_t num_results)
+{
+	struct crc_context *ctx;
+	size_t used, ret, i, curr_literal = 0;
+	long result;
+	uint32_t crcs[num_blocks(len1, block_size)];
+
+	crc_of_blocks(buffer1, len1, block_size, 32, crcs);
+	ctx = crc_context_new(block_size, 32, crcs, ARRAY_SIZE(crcs));
+
+	for (used = 0, i = 0; used < len2; used += ret) {
+		ret = crc_read_block(ctx, &result, buffer2+used, len2-used);
+
+		check_result(result, &curr_literal, results, num_results, &i);
+	}
+
+	while ((result = crc_read_flush(ctx)) != 0)
+		check_result(result, &curr_literal, results, num_results, &i);
+
+	check_finalized_result(curr_literal, results, num_results, &i);
+	
+	/* We must have achieved everything we expected. */
+	ok1(i == num_results);
+	crc_context_free(ctx);
+}
+
+int main(int argc, char *argv[])
+{
+	char *buffer1, *buffer2;
+	unsigned int i;
+	uint32_t crcs1[12], crcs2[12];
+
+	plan_tests(733);
+
+	buffer1 = calloc(1024, 1);
+	buffer2 = calloc(1024, 1);
+
+	/* Truncated end block test. */
+	crcs1[11] = 0xdeadbeef;
+	crc_of_blocks(buffer1, 1024, 100, 32, crcs1);
+	ok1(crcs1[11] == 0xdeadbeef);
+	crc_of_blocks(buffer2, 1024, 100, 32, crcs2);
+	ok1(memcmp(crcs1, crcs2, sizeof(crcs1[0])*11) == 0);
+
+	/* Fill with non-zero pattern, retest. */
+	for (i = 0; i < 1024; i++)
+		buffer1[i] = buffer2[i] = i + i/128;
+
+	crcs1[11] = 0xdeadbeef;
+	crc_of_blocks(buffer1, 1024, 100, 32, crcs1);
+	ok1(crcs1[11] == 0xdeadbeef);
+	crc_of_blocks(buffer2, 1024, 100, 32, crcs2);
+	ok1(memcmp(crcs1, crcs2, sizeof(crcs1[0])*11) == 0);
+
+	/* Check that it correctly masks bits. */
+	crc_of_blocks(buffer1, 1024, 128, 32, crcs1);
+	crc_of_blocks(buffer2, 1024, 128, 8, crcs2);
+	for (i = 0; i < 1024/128; i++)
+		ok1(crcs2[i] == (crcs1[i] & 0xFF));
+
+	/* Now test the "exact match" "round blocks" case. */
+	{
+		struct result res[] = {
+			{ BLOCK, 0 },
+			{ BLOCK, 1 },
+			{ BLOCK, 2 },
+			{ BLOCK, 3 },
+			{ BLOCK, 4 },
+			{ BLOCK, 5 },
+			{ BLOCK, 6 },
+			{ BLOCK, 7 } };
+		test_sync(buffer1, 1024, buffer2, 1024, 128,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now test the "exact match" with end block case. */
+	{
+		struct result res[] = {
+			{ BLOCK, 0 },
+			{ BLOCK, 1 },
+			{ BLOCK, 2 },
+			{ BLOCK, 3 },
+			{ BLOCK, 4 },
+			{ BLOCK, 5 },
+			{ BLOCK, 6 },
+			{ BLOCK, 7 },
+			{ BLOCK, 8 },
+			{ BLOCK, 9 },
+			{ BLOCK, 10 } };
+		test_sync(buffer1, 1024, buffer2, 1024, 100,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now test the "one byte append" "round blocks" case. */
+	{
+		struct result res[] = {
+			{ BLOCK, 0 },
+			{ BLOCK, 1 },
+			{ BLOCK, 2 },
+			{ BLOCK, 3 },
+			{ BLOCK, 4 },
+			{ BLOCK, 5 },
+			{ BLOCK, 6 },
+			{ LITERAL, 1 } };
+		test_sync(buffer1, 1024-128, buffer2, 1024-127, 128,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now test the "one byte append" with end block case. */
+	{
+		struct result res[] = {
+			{ BLOCK, 0 },
+			{ BLOCK, 1 },
+			{ BLOCK, 2 },
+			{ BLOCK, 3 },
+			{ BLOCK, 4 },
+			{ BLOCK, 5 },
+			{ BLOCK, 6 },
+			{ BLOCK, 7 },
+			{ BLOCK, 8 },
+			{ BLOCK, 9 },
+			{ BLOCK, 10 },
+			{ LITERAL, 1 } };
+		test_sync(buffer1, 1023, buffer2, 1024, 100,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now try changing one block at a time, check we get right results. */
+	for (i = 0; i < 1024/128; i++) {
+		unsigned int j;
+		struct result res[8];
+
+		/* Mess with block. */
+		memcpy(buffer2, buffer1, 1024);
+		buffer2[i * 128]++;
+
+		for (j = 0; j < ARRAY_SIZE(res); j++) {
+			if (j == i) {
+				res[j].type = LITERAL;
+				res[j].val = 128;
+			} else {
+				res[j].type = BLOCK;
+				res[j].val = j;
+			}
+		}
+
+		test_sync(buffer1, 1024, buffer2, 1024, 128,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now try shrinking one block at a time, check we get right results. */
+	for (i = 0; i < 1024/128; i++) {
+		unsigned int j;
+		struct result res[8];
+
+		/* Shrink block. */
+		memcpy(buffer2, buffer1, i * 128 + 64);
+		memcpy(buffer2 + i * 128 + 64, buffer1 + i * 128 + 65,
+		       1024 - (i * 128 + 65));
+
+		for (j = 0; j < ARRAY_SIZE(res); j++) {
+			if (j == i) {
+				res[j].type = LITERAL;
+				res[j].val = 127;
+			} else {
+				res[j].type = BLOCK;
+				res[j].val = j;
+			}
+		}
+
+		test_sync(buffer1, 1024, buffer2, 1023, 128,
+			  res, ARRAY_SIZE(res));
+	}
+
+	/* Now try shrinking one block at a time, check we get right results. */
+	for (i = 0; i < 1024/128; i++) {
+		unsigned int j;
+		struct result res[8];
+
+		/* Shrink block. */
+		memcpy(buffer2, buffer1, i * 128 + 64);
+		memcpy(buffer2 + i * 128 + 64, buffer1 + i * 128 + 65,
+		       1024 - (i * 128 + 65));
+
+		for (j = 0; j < ARRAY_SIZE(res); j++) {
+			if (j == i) {
+				res[j].type = LITERAL;
+				res[j].val = 127;
+			} else {
+				res[j].type = BLOCK;
+				res[j].val = j;
+			}
+		}
+
+		test_sync(buffer1, 1024, buffer2, 1023, 128,
+			  res, ARRAY_SIZE(res));
+	}
+
+	return exit_status();
+}

ccan/crcsync/test/run-crc.c

@@ -0,0 +1,36 @@
+#include "crcsync/crcsync.h"
+#include "crcsync/crcsync.c"
+#include "tap/tap.h"
+
+int main(int argc, char *argv[])
+{
+	char buffer[1024];
+	unsigned int i, j;
+	uint32_t crcs[12] = { 0xFFFFF, 0xdeadf00d };
+
+	plan_tests(3 + 8192);
+
+	/* Simple test (we know currently crc of 0s is 0) */
+	memset(buffer, 0, sizeof(buffer));
+	crc_of_blocks(buffer, sizeof(buffer), sizeof(buffer), 32, crcs);
+	ok1(crcs[0] == 0);
+	crc_of_blocks(buffer, sizeof(buffer), sizeof(buffer)/2, 32, crcs);
+	ok1(crcs[0] == 0);
+	ok1(crcs[1] == 0);
+
+	/* We know they're using crc32c. */
+	for (i = 0; i < sizeof(buffer); i++) {
+		buffer[i] = i;
+		crc_of_blocks(buffer, sizeof(buffer), sizeof(buffer)/7,
+			      32, crcs);
+		for (j = 0; j < sizeof(buffer); j += sizeof(buffer)/7) {
+			unsigned int len = sizeof(buffer)/7;
+			if (j + len > sizeof(buffer))
+				len = sizeof(buffer) - j;
+			
+			ok1(crc32c(0, buffer + j, len) == crcs[j/(sizeof(buffer)/7)]);
+		}
+	}
+
+	return exit_status();
+}

ccan/crcsync/test/run-roll.c

@@ -0,0 +1,38 @@
+#include "crcsync/crcsync.h"
+#include "crcsync/crcsync.c"
+#include "tap/tap.h"
+#include <stdlib.h>
+#include <stdbool.h>
+
+/* FIXME: ccanize. */
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+static void test_roll(unsigned int wsize)
+{
+	uint8_t data[wsize * 2];
+	uint32_t uncrc_tab[256];
+	unsigned int i;
+
+	init_uncrc_tab(uncrc_tab, wsize);
+
+	for (i = 0; i < ARRAY_SIZE(data); i++)
+		data[i] = random();
+
+	for (i = 1; i < ARRAY_SIZE(data) - wsize; i++) {
+		uint32_t rollcrc, crc;
+
+		crc = crc32c(0, data+i, wsize);
+		rollcrc = crc_roll(crc32c(0, data+i-1, wsize),
+				   data[i-1], data[i+wsize-1], uncrc_tab);
+
+		ok(crc == rollcrc, "wsize %u, i %u", wsize, i);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	plan_tests(100 - 1 + 128 - 1);
+	test_roll(100);
+	test_roll(128);
+	return exit_status();
+}