Add int128 randomized tests

Author: sipa

src/int128.h

@@ -12,6 +12,9 @@
 #    error "Please select int128 implementation"
 #  endif
 
+/* Construct an unsigned 128-bit value from a high and a low 64-bit value. */
+static SECP256K1_INLINE void secp256k1_u128_load(secp256k1_uint128 *r, uint64_t hi, uint64_t lo);
+
 /* Multiply two unsigned 64-bit values a and b and write the result to r. */
 static SECP256K1_INLINE void secp256k1_u128_mul(secp256k1_uint128 *r, uint64_t a, uint64_t b);
 
@@ -44,6 +47,9 @@ static SECP256K1_INLINE void secp256k1_u128_from_u64(secp256k1_uint128 *r, uint6
  */
 static SECP256K1_INLINE int secp256k1_u128_check_bits(const secp256k1_uint128 *r, unsigned int n);
 
+/* Construct an signed 128-bit value from a high and a low 64-bit value. */
+static SECP256K1_INLINE void secp256k1_i128_load(secp256k1_int128 *r, int64_t hi, uint64_t lo);
+
 /* Multiply two signed 64-bit values a and b and write the result to r. */
 static SECP256K1_INLINE void secp256k1_i128_mul(secp256k1_int128 *r, int64_t a, int64_t b);
 

src/int128_native_impl.h

@@ -3,6 +3,10 @@
 
 #include "int128.h"
 
+static SECP256K1_INLINE void secp256k1_u128_load(secp256k1_uint128 *r, uint64_t hi, uint64_t lo) {
+    *r = (((uint128_t)hi) << 64) + lo;
+}
+
 static SECP256K1_INLINE void secp256k1_u128_mul(secp256k1_uint128 *r, uint64_t a, uint64_t b) {
    *r = (uint128_t)a * b;
 }
@@ -37,6 +41,10 @@ static SECP256K1_INLINE int secp256k1_u128_check_bits(const secp256k1_uint128 *r
    return (*r >> n == 0);
 }
 
+static SECP256K1_INLINE void secp256k1_i128_load(secp256k1_int128 *r, int64_t hi, uint64_t lo) {
+    *r = (((uint128_t)(uint64_t)hi) << 64) + lo;
+}
+
 static SECP256K1_INLINE void secp256k1_i128_mul(secp256k1_int128 *r, int64_t a, int64_t b) {
    *r = (int128_t)a * b;
 }

src/int128_struct_impl.h

@@ -44,6 +44,11 @@ static SECP256K1_INLINE int64_t secp256k1_mul128(int64_t a, int64_t b, int64_t*
 }
 #endif
 
+static SECP256K1_INLINE void secp256k1_u128_load(secp256k1_uint128 *r, uint64_t hi, uint64_t lo) {
+    r->hi = hi;
+    r->lo = lo;
+}
+
 static SECP256K1_INLINE void secp256k1_u128_mul(secp256k1_uint128 *r, uint64_t a, uint64_t b) {
    r->lo = secp256k1_umul128(a, b, &r->hi);
 }
@@ -93,6 +98,11 @@ static SECP256K1_INLINE int secp256k1_u128_check_bits(const secp256k1_uint128 *r
                   : r->hi == 0 && r->lo >> n == 0;
 }
 
+static SECP256K1_INLINE void secp256k1_i128_load(secp256k1_int128 *r, int64_t hi, uint64_t lo) {
+    r->hi = hi;
+    r->lo = lo;
+}
+
 static SECP256K1_INLINE void secp256k1_i128_mul(secp256k1_int128 *r, int64_t a, int64_t b) {
    int64_t hi;
    r->lo = (uint64_t)secp256k1_mul128(a, b, &hi);