64 lines
1.2 KiB
V
64 lines
1.2 KiB
V
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// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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module rand
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import(
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math
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encoding.binary
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)
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pub fn read_u64(max u64) u64? {
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if max <= u64(0) {
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return error('crypto.rand: argument to read_u64 is <= 0')
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}
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// bitlen := int(math.floor(math.log2(f64(max))+1))
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bitlen := int(math.floor(math.log(f64(max))/math.log(2)) + 1)
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if bitlen == 0 {
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return u64(0)
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}
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k := (bitlen + 7) / 8
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mut b := u64(bitlen % 8)
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if b == u64(0) {
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b = u64(8)
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}
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mut n := u64(0)
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for {
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mut bytes := read(k) or {
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return error(err)
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}
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bytes[0] &= byte(int(u64(1)<<b) - 1)
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x := bytes_to_u64(bytes)
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n = x[0]
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if x.len > 1 {
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n = u64(u32(x[1])<<u32(32)) | n
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}
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if int(n) < 0 {
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n = -n
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}
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if n < max {
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return n
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}
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}
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return n
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}
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fn bytes_to_u64(b []byte) []u64 {
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mut z := [u64(0)].repeat((b.len + 8 - 1) / 8)
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mut i := b.len
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for k := 0; i >= 8; k++ {
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z[k] = binary.big_endian_u64(b.slice(i-8, i))
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i -= 8
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}
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if i > 0 {
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mut d := u64(0)
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for s := u64(0); i > 0; s += u64(8) {
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d |= u64(u64(b[i-1]) << s)
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i--
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}
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z[z.len-1] = d
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}
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return z
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}
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