Merge #12351: Libraries: Use correct type ; avoid compiler warnings.

a25cb0f Use ptrdiff_t type to more precisely indicate usage and avoid compiler warnings. (murrayn)

Pull request description:

  ptrdiff_t is a more strictly correct type, and gets rid of compiler warnings.

Tree-SHA512: 39718a5cdc10e698f14185f4622a9b439728bce619bd8b3a86f2b99ed5b056cf5a8545a3e5c4bc8a6a01b845fb73510036cee5e6d2629c58df26be692a957fba

Author: laanwj

src/key.cpp

@@ -44,15 +44,15 @@ static int ec_privkey_import_der(const secp256k1_context* ctx, unsigned char *ou
     if (end - privkey < 1 || !(*privkey & 0x80u)) {
         return 0;
     }
-    size_t lenb = *privkey & ~0x80u; privkey++;
+    ptrdiff_t lenb = *privkey & ~0x80u; privkey++;
     if (lenb < 1 || lenb > 2) {
         return 0;
     }
     if (end - privkey < lenb) {
         return 0;
     }
     /* sequence length */
-    size_t len = privkey[lenb-1] | (lenb > 1 ? privkey[lenb-2] << 8 : 0u);
+    ptrdiff_t len = privkey[lenb-1] | (lenb > 1 ? privkey[lenb-2] << 8 : 0u);
     privkey += lenb;
     if (end - privkey < len) {
         return 0;
@@ -66,7 +66,7 @@ static int ec_privkey_import_der(const secp256k1_context* ctx, unsigned char *ou
     if (end - privkey < 2 || privkey[0] != 0x04u) {
         return 0;
     }
-    size_t oslen = privkey[1];
+    ptrdiff_t oslen = privkey[1];
     privkey += 2;
     if (oslen > 32 || end - privkey < oslen) {
         return 0;