Refactor! Split the builder macros into a couple more places, and shift to From/Into instead of from_xxx and to_xxx.

src/cryptonum/barrett.rs

@@ -0,0 +1,112 @@
+macro_rules! derive_barrett
+{
+    ($type: ident, $barrett: ident, $count: expr) => {
+        impl CryptoNumFastMod for $type {
+            type BarrettMu = $barrett;
+
+            fn barrett_mu(&self) -> Option<$barrett> {
+                // Step #0: Don't divide by 0.
+                if self.is_zero() {
+                    return None
+                }
+                // Step #1: Compute k.
+                let mut k = $count;
+                while self.contents[k - 1] == 0 { k -= 1 };
+                // Step #2: The algorithm below only works if x has at most 2k
+                // digits, so if k*2 < count, abort this whole process.
+                if (k * 2) < $count {
+                    return None
+                }
+                // Step #2: Compute floor(b^2k / m), where m is this value.
+                let mut widebody_b2k  = [0; ($count * 2) + 1];
+                let mut widebody_self = [0; ($count * 2) + 1];
+                let mut quotient      = [0; ($count * 2) + 1];
+                let mut remainder     = [0; ($count * 2) + 1];
+                widebody_b2k[$count * 2] = 1;
+                for i in 0..k {
+                    widebody_self[i] = self.contents[i];
+                }
+                generic_div(&widebody_b2k, &widebody_self,
+                            &mut quotient, &mut remainder);
+                let mut result        = [0; $count + 1];
+                for (idx, val) in quotient.iter().enumerate() {
+                    if idx < ($count + 1) {
+                        result[idx] = *val;
+                    } else {
+                        if quotient[idx] != 0 {
+                            return None;
+                        }
+                    }
+                }
+                Some($barrett{k: k, progenitor: self.clone(), contents: result})
+            }
+
+            fn fastmod(&self, mu: &$barrett) -> $type {
+                // This algorithm is from our friends at the Handbook of
+                // Applied Cryptography, Chapter 14, Algorithm 14.42.
+                // Step #0:
+                //    Expand x so that it has the same size as the Barrett
+                //    value.
+                let mut x = [0; $count + 1];
+                for i in 0..$count {
+                    x[i] = self.contents[i];
+                }
+                // Step #1:
+                //    q1 <- floor(x / b^(k-1))
+                let mut q1 = x.clone();
+                generic_shr(&mut q1, &x, 64 * (mu.k - 1));
+                //    q2 <- q1 * mu
+                let q2 = expanding_mul(&q1, &mu.contents);
+                //    q3 <- floor(q2 / b^(k+1))
+                let mut q3big = q2.clone();
+                generic_shr(&mut q3big, &q2, 64 * (mu.k + 1));
+                let mut q3 = [0; $count + 1];
+                for (idx, val) in q3big.iter().enumerate() {
+                    if idx <= $count {
+                        q3[idx] = *val;
+                    } else {
+                        assert_eq!(*val, 0);
+                    }
+                }
+                // Step #2:
+                //    r1 <- x mod b^(k+1)
+                let mut r1 = x.clone();
+                for i in mu.k..($count+1) {
+                    r1[i] = 0;
+                }
+                //    r2 <- q3 * m mod b^(k+1)
+                let mut moddedm = [0; $count + 1];
+                for i in 0..mu.k {
+                    moddedm[i] = mu.progenitor.contents[i];
+                }
+                let mut r2 = q3.clone();
+                generic_mul(&mut r2, &q3, &moddedm);
+                //    r  <- r1 - r2
+                let mut r = r1.clone();
+                generic_sub(&mut r, &r2);
+                let is_negative = !ge(&r1, &r2);
+                // Step #3:
+                //    if r < 0 then r <- r + b^(k + 1)
+                if is_negative {
+                    let mut bk1 = [0; $count + 1];
+                    bk1[mu.k] = 1;
+                    generic_add(&mut r, &bk1);
+                }
+                // Step #4:
+                //    while r >= m do: r <- r - m.
+                while ge(&r, &moddedm) {
+                    generic_sub(&mut r, &moddedm);
+                }
+                // Step #5:
+                //    return r
+                let mut retval = [0; $count];
+                for i in 0..$count {
+                    retval[i] = r[i];
+                }
+                assert_eq!(r[$count], 0);
+                $type{ contents: retval }
+            }
+        }
+    }
+}
+