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128 lines
3.7 KiB
V
128 lines
3.7 KiB
V
// Copyright (c) 2019-2022 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 sys
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import math.bits
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import rand.buffer
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import rand.seed
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// Implementation note:
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// ====================
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// C.rand returns a pseudorandom integer from 0 (inclusive) to C.RAND_MAX (exclusive)
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// C.rand() is okay to use within its defined range.
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// (See: https://web.archive.org/web/20180801210127/http://eternallyconfuzzled.com/arts/jsw_art_rand.aspx)
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// The problem is, this value varies with the libc implementation. On windows,
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// for example, RAND_MAX is usually a measly 32767, whereas on (newer) linux it's generally
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// 2147483647. The repetition period also varies wildly. In order to provide more entropy
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// without altering the underlying algorithm too much, this implementation simply
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// requests for more random bits until the necessary width for the integers is achieved.
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pub const seed_len = 1
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const (
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rand_limit = u64(C.RAND_MAX)
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rand_bitsize = bits.len_64(rand_limit)
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rand_bytesize = rand_bitsize / 8
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u16_iter_count = calculate_iterations_for(16)
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u32_iter_count = calculate_iterations_for(32)
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u64_iter_count = calculate_iterations_for(64)
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)
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fn calculate_iterations_for(bits int) int {
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base := bits / sys.rand_bitsize
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extra := if bits % sys.rand_bitsize == 0 { 0 } else { 1 }
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return base + extra
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}
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// SysRNG is the PRNG provided by default in the libc implementiation that V uses.
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pub struct SysRNG {
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buffer.PRNGBuffer
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mut:
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seed u32 = seed.time_seed_32()
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}
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// r.seed() sets the seed of the accepting SysRNG to the given data.
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pub fn (mut r SysRNG) seed(seed_data []u32) {
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if seed_data.len != 1 {
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eprintln('SysRNG needs one 32-bit unsigned integer as the seed.')
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exit(1)
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}
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r.seed = seed_data[0]
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C.srand(r.seed)
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}
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// r.default_rand() exposes the default behavior of the system's RNG
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// (equivalent to calling C.rand()). Recommended for testing/comparison
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// b/w V and other languages using libc and not for regular use.
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// This is also a one-off feature of SysRNG, similar to the global seed
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// situation. Other generators will not have this.
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[inline]
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pub fn (r SysRNG) default_rand() int {
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return C.rand()
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}
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// byte returns a uniformly distributed pseudorandom 8-bit unsigned positive `byte`.
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[inline]
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pub fn (mut r SysRNG) u8() u8 {
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if r.bytes_left >= 1 {
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r.bytes_left -= 1
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value := u8(r.buffer)
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r.buffer >>= 8
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return value
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}
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r.buffer = u64(r.default_rand())
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r.bytes_left = sys.rand_bytesize - 1
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value := u8(r.buffer)
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r.buffer >>= 8
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return value
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}
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// u16 returns a uniformly distributed pseudorandom 16-bit unsigned positive `u16`.
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[inline]
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pub fn (mut r SysRNG) u16() u16 {
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if r.bytes_left >= 2 {
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r.bytes_left -= 2
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value := u16(r.buffer)
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r.buffer >>= 16
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return value
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}
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mut result := u16(C.rand())
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for i in 1 .. sys.u16_iter_count {
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result = result ^ (u16(C.rand()) << (sys.rand_bitsize * i))
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}
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return result
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}
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// u32 returns a uniformly distributed pseudorandom 32-bit unsigned positive `u32`.
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[inline]
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pub fn (r SysRNG) u32() u32 {
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mut result := u32(C.rand())
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for i in 1 .. sys.u32_iter_count {
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result = result ^ (u32(C.rand()) << (sys.rand_bitsize * i))
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}
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return result
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}
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// u64 returns a uniformly distributed pseudorandom 64-bit unsigned positive `u64`.
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[inline]
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pub fn (r SysRNG) u64() u64 {
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mut result := u64(C.rand())
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for i in 1 .. sys.u64_iter_count {
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result = result ^ (u64(C.rand()) << (sys.rand_bitsize * i))
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}
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return result
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}
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// block_size returns the number of bits that the RNG can produce in a single iteration.
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[inline]
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pub fn (r SysRNG) block_size() int {
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return sys.rand_bitsize
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}
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// free should be called when the generator is no longer needed
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[unsafe]
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pub fn (mut rng SysRNG) free() {
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unsafe { free(rng) }
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}
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