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Added comments to the delta diff code

pull/166/head
Daniele Lacamera 2022-01-03 13:03:36 +01:00
parent c76166f6ea
commit 21c57be53e
1 changed files with 27 additions and 0 deletions
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27
src/delta.c
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@ -223,18 +223,28 @@ int wb_diff(WB_DIFF_CTX *ctx, uint8_t *patch, uint32_t len)
break;
if ((memcmp(pa, (ctx->src_b + ctx->off_b), BLOCK_HDR_SIZE) == 0)) {
uint32_t b_start;
/* Identical areas of BLOCK_HDR_SIZE bytes match between the images.
* initialize match_len; blk_start is the relative offset within
* the src image.
*/
match_len = BLOCK_HDR_SIZE;
blk_start = pa - ctx->src_a;
b_start = ctx->off_b;
pa+= BLOCK_HDR_SIZE;
ctx->off_b += BLOCK_HDR_SIZE;
while (*pa == *(ctx->src_b + ctx->off_b)) {
/* Extend matching block if possible, as long as the
* identical sequence continues.
*/
if ((uint32_t)(pa + 1 - ctx->src_a) >= ctx->size_a) {
/* Stop matching if the source image size limit is hit. */
break;
}
if ((b_start / WOLFBOOT_SECTOR_SIZE) < ((ctx->off_b + 1) / WOLFBOOT_SECTOR_SIZE)) {
/* Stop matching when the sector bound is hit. */
break;
}
/* Increase match len, test next byte */
pa++;
ctx->off_b++;
match_len++;
@ -257,18 +267,35 @@ int wb_diff(WB_DIFF_CTX *ctx, uint8_t *patch, uint32_t len)
uint32_t pb_end = page_start * WOLFBOOT_SECTOR_SIZE;
pb = ctx->src_b;
while (((uint32_t)(pb - ctx->src_b) < pb_end) && (p_off < len)) {
/* Check image boundary */
if ((ctx->size_b - ctx->off_b) < BLOCK_HDR_SIZE)
break;
if ((uint32_t)(ctx->size_b - (pb - ctx->src_b)) < BLOCK_HDR_SIZE)
break;
/* Don't try matching backwards if the distance between the two
* blocks is smaller than one sector.
*/
if (WOLFBOOT_SECTOR_SIZE > (pb - ctx->src_b) - (page_start * WOLFBOOT_SECTOR_SIZE))
break;
if ((memcmp(pb, (ctx->src_b + ctx->off_b), BLOCK_HDR_SIZE) == 0)) {
/* A match was found between the current pointer and a
* previously patched area in the resulting image.
* Initialize match_len and set the blk_start to the beginning
* of the matching area in the image.
*/
match_len = BLOCK_HDR_SIZE;
blk_start = pb - ctx->src_b;
pb+= BLOCK_HDR_SIZE;
ctx->off_b += BLOCK_HDR_SIZE;
while (*pb == *(ctx->src_b + ctx->off_b)) {
/* Extend match as long as the areas have the
* same content. Block skipping in this case is
* not a problem since the distance between the patched
* area and the area to patch is always larger than one
* block size.
*/
pb++;
if ((uint32_t)(pb - ctx->src_b) >= pb_end) {
pb--;