math: new consts + helpers funcs for string to int / float

vlib/math/bits.v

@@ -0,0 +1,58 @@
+// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module math
+
+const (
+	uvnan     = 0x7FF8000000000001
+	uvinf     = 0x7FF0000000000000
+	uvneginf  = 0xFFF0000000000000
+	uvone     = 0x3FF0000000000000
+	mask      = 0x7FF
+	shift     = 64 - 11 - 1
+	bias      = 1023
+	sign_mask = u64(u64(1) << 63)
+	frac_mask = u64(u64(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 { uvinf } else { uvneginf }
+	return f64_from_bits(v)
+}
+
+// nan returns an IEEE 754 ``not-a-number'' value.
+pub fn nan() f64 { return f64_from_bits(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.
+	// To avoid the floating-point hardware, could use:
+	//	x := f64_bits(f);
+	//	return u32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
+	return f != f
+}
+
+// is_inf reports whether f is an infinity, according to sign.
+// If sign > 0, is_inf reports whether f is positive infinity.
+// If sign < 0, is_inf reports whether f is negative infinity.
+// If sign == 0, is_inf reports whether f is either infinity.
+pub fn is_inf(f f64, sign int) bool {
+	// Test for infinity by comparing against maximum float.
+	// To avoid the floating-point hardware, could use:
+	//	x := f64_bits(f);
+	//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
+	return (sign >= 0 && f > max_f64) || (sign <= 0 && f < -max_f64)
+}
+
+// NOTE: (joe-c) exponent notation is borked
+// 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
+// }