vlib/math: Add a pure V backend for vlib/math (#11267)

vlib/math/pow.v

@@ -0,0 +1,37 @@
+module math
+
+const (
+	pow10tab      = [f64(1e+00), 1e+01, 1e+02, 1e+03, 1e+04, 1e+05, 1e+06, 1e+07, 1e+08, 1e+09,
+		1e+10, 1e+11, 1e+12, 1e+13, 1e+14, 1e+15, 1e+16, 1e+17, 1e+18, 1e+19, 1e+20, 1e+21, 1e+22,
+		1e+23, 1e+24, 1e+25, 1e+26, 1e+27, 1e+28, 1e+29, 1e+30, 1e+31]
+	pow10postab32 = [f64(1e+00), 1e+32, 1e+64, 1e+96, 1e+128, 1e+160, 1e+192, 1e+224, 1e+256, 1e+288]
+	pow10negtab32 = [f64(1e-00), 1e-32, 1e-64, 1e-96, 1e-128, 1e-160, 1e-192, 1e-224, 1e-256, 1e-288,
+		1e-320,
+	]
+)
+
+// powf returns base raised to the provided power. (float32)
+[inline]
+pub fn powf(a f32, b f32) f32 {
+	return f32(pow(a, b))
+}
+
+// pow10 returns 10**n, the base-10 exponential of n.
+//
+// special cases are:
+// pow10(n) =    0 for n < -323
+// pow10(n) = +inf for n > 308
+pub fn pow10(n int) f64 {
+	if 0 <= n && n <= 308 {
+		return math.pow10postab32[u32(n) / 32] * math.pow10tab[u32(n) % 32]
+	}
+	if -323 <= n && n <= 0 {
+		return math.pow10negtab32[u32(-n) / 32] / math.pow10tab[u32(-n) % 32]
+	}
+	// n < -323 || 308 < n
+	if n > 0 {
+		return inf(1)
+	}
+	// n < -323
+	return 0.0
+}