v/vlib/crypto/rand/utils.v

64 lines
1.2 KiB
V
Raw Normal View History

// 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 rand
import(
math
encoding.binary
)
pub fn read_u64(max u64) u64? {
if max <= u64(0) {
return error('crypto.rand: argument to read_u64 is <= 0')
}
// bitlen := int(math.floor(math.log2(f64(max))+1))
bitlen := int(math.floor(math.log(f64(max))/math.log(2)) + 1)
if bitlen == 0 {
return u64(0)
}
k := (bitlen + 7) / 8
mut b := u64(bitlen % 8)
if b == u64(0) {
b = u64(8)
}
mut n := u64(0)
for {
mut bytes := read(k) or {
return error(err)
}
bytes[0] &= byte(int(u64(1)<<b) - 1)
x := bytes_to_u64(bytes)
n = x[0]
if x.len > 1 {
n = u64(u32(x[1])<<u32(32)) | n
}
if int(n) < 0 {
n = -n
}
if n < max {
return n
}
}
return n
}
fn bytes_to_u64(b []byte) []u64 {
mut z := [u64(0)].repeat((b.len + 8 - 1) / 8)
mut i := b.len
for k := 0; i >= 8; k++ {
z[k] = binary.big_endian_u64(b.slice(i-8, i))
i -= 8
}
if i > 0 {
mut d := u64(0)
for s := u64(0); i > 0; s += u64(8) {
d |= u64(u64(b[i-1]) << s)
i--
}
z[z.len-1] = d
}
return z
}