mirror of
https://github.com/vlang/v.git
synced 2023-08-10 21:13:21 +03:00
65 lines
2.0 KiB
V
65 lines
2.0 KiB
V
module math
|
|
|
|
// The vlang code is a modified version of the original C code from
|
|
// http://www.netlib.org/fdlibm/s_cbrt.c and came with this notice.
|
|
//
|
|
// ====================================================
|
|
// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
|
|
//
|
|
// Developed at SunSoft, a Sun Microsystems, Inc. business.
|
|
// Permission to use, copy, modify, and distribute this
|
|
// software is freely granted, provided that this notice
|
|
// is preserved.
|
|
// ====================================================
|
|
|
|
// cbrt returns the cube root of a.
|
|
//
|
|
// special cases are:
|
|
// cbrt(±0) = ±0
|
|
// cbrt(±inf) = ±inf
|
|
// cbrt(nan) = nan
|
|
pub fn cbrt(a f64) f64 {
|
|
mut x := a
|
|
b1 := 715094163 // (682-0.03306235651)*2**20
|
|
b2 := 696219795 // (664-0.03306235651)*2**20
|
|
c := 5.42857142857142815906e-01 // 19/35 = 0x3FE15F15F15F15F1
|
|
d := -7.05306122448979611050e-01 // -864/1225 = 0xBFE691DE2532C834
|
|
e_ := 1.41428571428571436819e+00 // 99/70 = 0x3FF6A0EA0EA0EA0F
|
|
f := 1.60714285714285720630e+00 // 45/28 = 0x3FF9B6DB6DB6DB6E
|
|
g := 3.57142857142857150787e-01 // 5/14 = 0x3FD6DB6DB6DB6DB7
|
|
smallest_normal := 2.22507385850720138309e-308 // 2**-1022 = 0x0010000000000000
|
|
if x == 0.0 || is_nan(x) || is_inf(x, 0) {
|
|
return x
|
|
}
|
|
mut sign := false
|
|
if x < 0 {
|
|
x = -x
|
|
sign = true
|
|
}
|
|
// rough cbrt to 5 bits
|
|
mut t := f64_from_bits(f64_bits(x) / u64(3) + (u64(b1) << 32))
|
|
if x < smallest_normal {
|
|
// subnormal number
|
|
t = f64(u64(1) << 54) // set t= 2**54
|
|
t *= x
|
|
t = f64_from_bits(f64_bits(t) / u64(3) + (u64(b2) << 32))
|
|
}
|
|
// new cbrt to 23 bits
|
|
mut r := t * t / x
|
|
mut s := c + r * t
|
|
t *= g + f / (s + e_ + d / s)
|
|
// chop to 22 bits, make larger than cbrt(x)
|
|
t = f64_from_bits(f64_bits(t) & (u64(0xffffffffc) << 28) + (u64(1) << 30))
|
|
// one step newton iteration to 53 bits with error less than 0.667ulps
|
|
s = t * t // t*t is exact
|
|
r = x / s
|
|
w := t + t
|
|
r = (r - t) / (w + r) // r-s is exact
|
|
t = t + t * r
|
|
// restore the sign bit
|
|
if sign {
|
|
t = -t
|
|
}
|
|
return t
|
|
}
|