39 lines
781 B
V
39 lines
781 B
V
|
module math
|
||
|
|
|
||
|
|
// scalbn scales x by FLT_RADIX raised to the power of n, returning the same as:
|
||
|
|
// scalbn(x,n) = x * FLT_RADIX ** n
|
||
|
|
pub fn scalbn(x f64, n_ int) f64 {
|
||
|
|
mut n := n_
|
||
|
|
x1p1023 := f64_from_bits(u64(0x7fe0000000000000))
|
||
|
|
x1p53 := f64_from_bits(u64(0x4340000000000000))
|
||
|
|
x1p_1022 := f64_from_bits(u64(0x0010000000000000))
|
||
|
|
|
||
|
|
mut y := x
|
||
|
|
if n > 1023 {
|
||
|
|
y *= x1p1023
|
||
|
|
n -= 1023
|
||
|
|
if n > 1023 {
|
||
|
|
y *= x1p1023
|
||
|
|
n -= 1023
|
||
|
|
if n > 1023 {
|
||
|
|
n = 1023
|
||
|
|
}
|
||
|
|
}
|
||
|
|
} else if n < -1022 {
|
||
|
|
/*
|
||
|
|
make sure final n < -53 to avoid double
|
||
|
|
rounding in the subnormal range
|
||
|
|
*/
|
||
|
|
y *= x1p_1022 * x1p53
|
||
|
|
n += 1022 - 53
|
||
|
|
if n < -1022 {
|
||
|
|
y *= x1p_1022 * x1p53
|
||
|
|
n += 1022 - 53
|
||
|
|
if n < -1022 {
|
||
|
|
n = -1022
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return y * f64_from_bits(u64((0x3ff + n)) << 52)
|
||
|
|
}
|