Force inlining, use ctz to reduce dependency in loop.

Author: two-horned

lib/std/math/egcd.zig

@@ -15,7 +15,7 @@ pub fn ExtendedGreatestCommonDivisor(S: anytype) type {
     };
 }
 
-fn egcd_helper(other: anytype, odd: anytype, shift: anytype) [3]@TypeOf(other, odd) {
+inline fn egcd_helper(other: anytype, odd: anytype, shift: anytype) [3]@TypeOf(other, odd) {
     const S = @TypeOf(other, odd);
     const toinv = @shrExact(other, @intCast(shift));
     const ctrl = @shrExact(odd, @intCast(shift));
@@ -26,16 +26,19 @@ fn egcd_helper(other: anytype, odd: anytype, shift: anytype) [3]@TypeOf(other, o
     var x = @abs(toinv);
     var y = @abs(ctrl);
 
-    while (x & 1 == 0) {
-        x = @shrExact(x, 1);
-        s = @shrExact(if (s & 1 == 0) s else s + ctrl, 1);
+    {
+        const xz = @ctz(x);
+        x = @shrExact(x, @intCast(xz));
+        for (0..xz) |_|
+            s = @shrExact(if (s & 1 == 0) s else s + ctrl, 1);
     }
 
     var y_minus_x = y -% x;
     while (y_minus_x != 0) : (y_minus_x = y -% x) {
         const t_minus_s = t - s;
         const copy_x = x;
         const copy_s = s;
+        const xz = @ctz(y_minus_x);
 
         s -= t;
         const carry = x < y;
@@ -46,10 +49,9 @@ fn egcd_helper(other: anytype, odd: anytype, shift: anytype) [3]@TypeOf(other, o
             s = t_minus_s;
             t = copy_s;
         }
-        while (x & 1 == 0) {
-            x = @shrExact(x, 1);
+        x = @shrExact(x, @intCast(xz));
+        for (0..xz) |_|
             s = @shrExact(if (s & 1 == 0) s else s + ctrl, 1);
-        }
     }
 
     y = @shlExact(y, @intCast(shift));
@@ -83,13 +85,12 @@ pub fn egcd(a: anytype, b: anytype) ExtendedGreatestCommonDivisor(@TypeOf(a, b))
 
     const xz = @ctz(x);
     const yz = @ctz(y);
-    const shift = @min(xz, yz);
 
     if (xz < yz) {
-        const gcd, const t, const s = egcd_helper(y, x, shift);
+        const gcd, const t, const s = egcd_helper(y, x, xz);
         return .{ .gcd = @intCast(gcd), .bezout_coeff_1 = s, .bezout_coeff_2 = t };
     } else {
-        const gcd, const s, const t = egcd_helper(x, y, shift);
+        const gcd, const s, const t = egcd_helper(x, y, yz);
         return .{ .gcd = @intCast(gcd), .bezout_coeff_1 = s, .bezout_coeff_2 = t };
     }
 }