Add fast paths for Math(f).pow (#1053)

Author: MaxGraey

std/assembly/math.ts

@@ -1180,6 +1180,18 @@ export namespace NativeMath {
   }
 
   export function pow(x: f64, y: f64): f64 { // see: musl/src/math/pow.c and SUN COPYRIGHT NOTICE above
+    // TODO: remove this fast pathes after introduced own mid-end IR with "stdlib call simplify" transforms
+    if (builtin_abs<f64>(y) <= 2) {
+      if (y ==  2.0) return x * x;
+      if (y ==  0.5) return select<f64>(Infinity, builtin_sqrt<f64>(x), builtin_abs<f64>(x) == Infinity);
+      if (y == -1.0) return 1 / x;
+      if (y == -0.5) {
+        if (x == 0.0) return Infinity;
+        return select<f64>(0, 1 / builtin_sqrt<f64>(x), builtin_abs<f64>(x) == Infinity);
+      }
+      if (y == 1.0) return x;
+      if (y == 0.0) return 1.0;
+    }
     if (ASC_SHRINK_LEVEL < 1) {
       return pow_lut(x, y);
     } else {
@@ -2564,6 +2576,18 @@ export namespace NativeMathf {
   }
 
   export function pow(x: f32, y: f32): f32 { // see: musl/src/math/powf.c and SUN COPYRIGHT NOTICE above
+    // TODO: remove this fast pathes after introduced own mid-end IR with "stdlib call simplify" transforms
+    if (builtin_abs<f32>(y) <= 2) {
+      if (y ==  2.0) return x * x;
+      if (y ==  0.5) return select<f32>(Infinity, builtin_sqrt<f32>(x), builtin_abs<f32>(x) == Infinity);
+      if (y == -1.0) return 1 / x;
+      if (y == -0.5) {
+        if (x == 0.0) return Infinity;
+        return select<f32>(0, 1 / builtin_sqrt<f32>(x), builtin_abs<f32>(x) == Infinity);
+      }
+      if (y == 1.0) return x;
+      if (y == 0.0) return 1.0;
+    }
     return powf_lut(x, y);
   }