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

vlib/math/bits.v

@@ -4,17 +4,29 @@
 module math
 
 const (
-	uvnan     = u64(0x7FF8000000000001)
-	uvinf     = u64(0x7FF0000000000000)
-	uvneginf  = u64(0xFFF0000000000000)
-	uvone     = u64(0x3FF0000000000000)
-	mask      = 0x7FF
-	shift     = 64 - 11 - 1
-	bias      = 1023
-	sign_mask = (u64(1) << 63)
-	frac_mask = ((u64(1) << u64(shift)) - u64(1))
+	uvnan                   = u64(0x7FF8000000000001)
+	uvinf                   = u64(0x7FF0000000000000)
+	uvneginf                = u64(0xFFF0000000000000)
+	uvone                   = u64(0x3FF0000000000000)
+	mask                    = 0x7FF
+	shift                   = 64 - 11 - 1
+	bias                    = 1023
+	normalize_smallest_mask = (u64(1) << 52)
+	sign_mask               = (u64(1) << 63)
+	frac_mask               = ((u64(1) << u64(shift)) - u64(1))
 )
 
+// inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
+pub fn inf(sign int) f64 {
+	v := if sign >= 0 { math.uvinf } else { math.uvneginf }
+	return f64_from_bits(v)
+}
+
+// nan returns an IEEE 754 ``not-a-number'' value.
+pub fn nan() f64 {
+	return f64_from_bits(math.uvnan)
+}
+
 // is_nan reports whether f is an IEEE 754 ``not-a-number'' value.
 pub fn is_nan(f f64) bool {
 	// IEEE 754 says that only NaNs satisfy f != f.
@@ -36,13 +48,16 @@ pub fn is_inf(f f64, sign int) bool {
 	return (sign >= 0 && f > max_f64) || (sign <= 0 && f < -max_f64)
 }
 
-// NOTE: (joe-c) exponent notation is borked
+pub fn is_finite(f f64) bool {
+	return !is_nan(f) && !is_inf(f, 0)
+}
+
 // normalize returns a normal number y and exponent exp
 // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
-// pub fn normalize(x f64) (f64, int) {
-// smallest_normal := 2.2250738585072014e-308 // 2**-1022
-// if abs(x) < smallest_normal {
-// return x * (1 << 52), -52
-// }
-// return x, 0
-// }
+pub fn normalize(x f64) (f64, int) {
+	smallest_normal := 2.2250738585072014e-308 // 2**-1022
+	if abs(x) < smallest_normal {
+		return x * math.normalize_smallest_mask, -52
+	}
+	return x, 0
+}