Avoid undefined shift behaviour

sipa · sipa · commit 9048def7c749 · 2014-12-03T18:10:52.000+01:00
diff --git a/src/scalar_4x64_impl.h b/src/scalar_4x64_impl.h
@@ -95,7 +95,7 @@ static void secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t
 
 static void secp256k1_scalar_add_bit(secp256k1_scalar_t *r, unsigned int bit) {
     VERIFY_CHECK(bit < 256);
-    uint128_t t = (uint128_t)r->d[0] + (((uint64_t)((bit >> 6) == 0)) << bit);
+    uint128_t t = (uint128_t)r->d[0] + (((uint64_t)((bit >> 6) == 0)) << (bit & 0x3F));
     r->d[0] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
     t += (uint128_t)r->d[1] + (((uint64_t)((bit >> 6) == 1)) << (bit & 0x3F));
     r->d[1] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
diff --git a/src/scalar_8x32_impl.h b/src/scalar_8x32_impl.h
@@ -133,7 +133,7 @@ static void secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t
 
 static void secp256k1_scalar_add_bit(secp256k1_scalar_t *r, unsigned int bit) {
     VERIFY_CHECK(bit < 256);
-    uint64_t t = (uint64_t)r->d[0] + (((uint32_t)((bit >> 5) == 0)) << bit);
+    uint64_t t = (uint64_t)r->d[0] + (((uint32_t)((bit >> 5) == 0)) << (bit & 0x1F));
     r->d[0] = t & 0xFFFFFFFFULL; t >>= 32;
     t += (uint64_t)r->d[1] + (((uint32_t)((bit >> 5) == 1)) << (bit & 0x1F));
     r->d[1] = t & 0xFFFFFFFFULL; t >>= 32;
