Improve md5 buffer storing concept

Author: adustm

features/mbedtls/targets/TARGET_STM/md5_alt.c

@@ -57,9 +57,6 @@ void mbedtls_md5_clone( mbedtls_md5_context *dst,
     *dst = *src;
 }
 
-/*
- * MD5 context setup
- */
 void mbedtls_md5_starts( mbedtls_md5_context *ctx )
 {
     /* HASH IP initialization */
@@ -78,47 +75,38 @@ void mbedtls_md5_process( mbedtls_md5_context *ctx, const unsigned char data[64]
     HAL_HASH_MD5_Accumulate(&ctx->hhash_md5, (uint8_t *)data, 64);
 }
 
-/*
- * MD5 process buffer
- */
 void mbedtls_md5_update( mbedtls_md5_context *ctx, const unsigned char *input, size_t ilen )
 {
-    unsigned char i=0;
-    int currentlen = ilen;
-    /* store mechanism to handle 64 bytes per 64 bytes */
-    if (currentlen == 0){ // change HW status is size if 0
+    size_t currentlen = ilen;
+    // store mechanism to handle 64 bytes per 64 bytes
+    if (currentlen == 0){ // only change HW status is size if 0
         if(ctx->hhash_md5.Phase == HAL_HASH_PHASE_READY)
         {
           /* Select the MD5 mode and reset the HASH processor core, so that the HASH will be ready to compute
              the message digest of a new message */
           HASH->CR |= HASH_ALGOSELECTION_MD5 | HASH_CR_INIT;
         }
         ctx->hhash_md5.Phase = HAL_HASH_PHASE_PROCESS;
-    }
-    while ((currentlen+ctx->sbuf_len) >=64) {
-        if (ctx->sbuf_len ==0) { /* straight forward */
-            mbedtls_md5_process(ctx, input+(i*64));
-        } else {
-            memcpy(ctx->sbuf+ctx->sbuf_len, input+(i*64),64-ctx->sbuf_len);
-            mbedtls_md5_process(ctx, ctx->sbuf);
-            memcpy(ctx->sbuf,input+(i+1)*64-ctx->sbuf_len, ctx->sbuf_len);
-            // ctx->sbuf_len remains the same
+    } else if (currentlen < (64-ctx->sbuf_len)) {
+        // only buffurize
+        memcpy(ctx->sbuf+ctx->sbuf_len, input, currentlen);
+        ctx->sbuf_len += currentlen;
+    } else {
+        // fill buffer and process it
+        memcpy(ctx->sbuf + ctx->sbuf_len, input, (64-ctx->sbuf_len));
+        currentlen -= (64-ctx->sbuf_len);
+        mbedtls_md5_process(ctx, ctx->sbuf);
+        // now process every input as long as it is %4 bytes
+        size_t iter = currentlen / 4;
+        HAL_HASH_MD5_Accumulate(&ctx->hhash_md5, (uint8_t *)(input+64-ctx->sbuf_len), (iter*4));
+        // sbuf is now fully accumulated, now copy 1 / 2 or 3 remaining bytes
+        ctx->sbuf_len = currentlen % 4;
+        if (ctx->sbuf_len !=0) {
+            memcpy(ctx->sbuf, input+iter, ctx->sbuf_len);
         }
-        currentlen -= 64;
-        i++;
     }
-    if (currentlen <0) {
-        currentlen +=64;
-    }
-    /* Store the remaining <64 values */
-    memcpy(ctx->sbuf+ctx->sbuf_len, input+(i*64), currentlen);
-    ctx->sbuf_len += currentlen;
-
 }
 
-/*
- * MD5 final digest
- */
 void mbedtls_md5_finish( mbedtls_md5_context *ctx, unsigned char output[16] )
 {
     if (ctx->sbuf_len > 0) {