lyb BUGFIX make sure written hash is not 0

Author: michalvasko

src/lyb.c

@@ -219,3 +219,26 @@ lyb_prepend_bits(void *buf, uint32_t count_bytes, uint8_t byte, uint8_t byte_bit
     /* prepend the bits from the byte */
     ((uint8_t *)buf)[0] |= byte & lyb_right_bit_mask(byte_bits);
 }
+
+uint32_t
+lyb_truncate_hash_nonzero(uint32_t hash, uint8_t hash_bits)
+{
+    uint32_t orig_hash = hash;
+    uint8_t offset;
+
+    assert(hash && !(hash_bits % 8));
+
+    offset = 0;
+    do {
+        hash = orig_hash;
+
+        /* truncate hash */
+        hash <<= (32 - offset) - hash_bits;
+        hash >>= 32 - hash_bits;
+
+        /* next offset */
+        offset += 8;
+    } while (!hash);
+
+    return hash;
+}

src/lyb.h

@@ -255,4 +255,15 @@ void lyb_right_shift(void *buf, uint32_t count_bytes, uint8_t shift);
  */
 void lyb_prepend_bits(void *buf, uint32_t count_bytes, uint8_t byte, uint8_t byte_bits);
 
+/**
+ * @brief Truncate a hash to rightmost bits and make sure it is non-zero.
+ *
+ * If these bits are all zeroes, next bits are used.
+ *
+ * @param[in] hash Hash to truncate.
+ * @param[in] hash_bits Size of the truncate hash in bits.
+ * @return Truncated non-zero hash.
+ */
+uint32_t lyb_truncate_hash_nonzero(uint32_t hash, uint8_t hash_bits);
+
 #endif /* LY_LYB_H_ */

src/parser_lyb.c

@@ -1542,9 +1542,7 @@ lyb_parse_header(struct lylyb_parse_ctx *lybctx)
         lybctx->empty_hash = 1;
     } else {
         /* truncate context hash to the same bit size */
-        cur_hash = ly_ctx_get_modules_hash(lybctx->ctx);
-        cur_hash <<= (sizeof cur_hash * 8) - LYB_HEADER_CTX_HASH_BITS;
-        cur_hash >>= (sizeof cur_hash * 8) - LYB_HEADER_CTX_HASH_BITS;
+        cur_hash = lyb_truncate_hash_nonzero(ly_ctx_get_modules_hash(lybctx->ctx), LYB_HEADER_CTX_HASH_BITS);
 
         if (data_hash != cur_hash) {
             LOGERR(lybctx->ctx, LY_EINVAL, "Different current LYB context modules hash compared to the one stored in the "

src/printer_lyb.c

@@ -634,7 +634,7 @@ lyb_print_header(struct lylyb_print_ctx *lybctx)
 
     /* context hash (is truncated), if not printing empty data */
     if (lybctx->ctx) {
-        hash = ly_ctx_get_modules_hash(lybctx->ctx);
+        hash = lyb_truncate_hash_nonzero(ly_ctx_get_modules_hash(lybctx->ctx), LYB_HEADER_CTX_HASH_BITS);
     } else {
         hash = 0;
     }