Merge #129

129: Fix the bit shifts at the end of Toom-3 r=cuviper a=cuviper

This fixes a regression from 64-bit `BigDigit` (#62).

Co-authored-by: Josh Stone <cuviper@gmail.com>

Author: bors[bot]

src/algorithms.rs

@@ -517,11 +517,12 @@ fn mac3(acc: &mut [BigDigit], b: &[BigDigit], c: &[BigDigit]) {
         // Recomposition. The coefficients of the polynomial are now known.
         //
         // Evaluate at w(t) where t is our given base to get the result.
+        let bits = big_digit::BITS * i;
         let result = r0
-            + (comp1 << (32 * i))
-            + (comp2 << (2 * 32 * i))
-            + (comp3 << (3 * 32 * i))
-            + (r4 << (4 * 32 * i));
+            + (comp1 << bits)
+            + (comp2 << (2 * bits))
+            + (comp3 << (3 * bits))
+            + (r4 << (4 * bits));
         let result_pos = result.to_biguint().unwrap();
         add2(&mut acc[..], &result_pos.data);
     }

tests/torture.rs

@@ -8,10 +8,14 @@ use num_bigint::RandBigInt;
 use num_traits::Zero;
 use rand::prelude::*;
 
+fn get_rng() -> SmallRng {
+    let seed = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
+    SmallRng::from_seed(seed)
+}
+
 fn test_mul_divide_torture_count(count: usize) {
     let bits_max = 1 << 12;
-    let seed = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
-    let mut rng = SmallRng::from_seed(seed);
+    let mut rng = get_rng();
 
     for _ in 0..count {
         // Test with numbers of random sizes:
@@ -33,11 +37,40 @@ fn test_mul_divide_torture_count(count: usize) {
 
 #[test]
 fn test_mul_divide_torture() {
-    test_mul_divide_torture_count(1000);
+    test_mul_divide_torture_count(1_000);
 }
 
 #[test]
 #[ignore]
 fn test_mul_divide_torture_long() {
-    test_mul_divide_torture_count(1000000);
+    test_mul_divide_torture_count(1_000_000);
+}
+
+fn test_factored_mul_torture_count(count: usize) {
+    let bits = 1 << 16;
+    let mut rng = get_rng();
+
+    for _ in 0..count {
+        let w = rng.gen_biguint(bits);
+        let x = rng.gen_biguint(bits);
+        let y = rng.gen_biguint(bits);
+        let z = rng.gen_biguint(bits);
+
+        let prod1 = (&w * &x) * (&y * &z);
+        let prod2 = (&w * &y) * (&x * &z);
+        let prod3 = (&w * &z) * (&x * &y);
+        assert_eq!(prod1, prod2);
+        assert_eq!(prod2, prod3);
+    }
+}
+
+#[test]
+fn test_factored_mul_torture() {
+    test_factored_mul_torture_count(50);
+}
+
+#[test]
+#[ignore]
+fn test_factored_mul_torture_long() {
+    test_factored_mul_torture_count(1_000);
 }