Commit 45860e92 authored by Peter Limkilde Svendsen's avatar Peter Limkilde Svendsen Committed by jD91mZM2

Implement LCG pseudorandom number functions

parent 06ab5b7d
//! Helper functions for pseudorandom number generation using LCG, see http://pubs.opengroup.org/onlinepubs/7908799/xsh/drand48.html
use platform::types::*;
/* The current element of the linear congruential generator's sequence. Any
* function that sets this variable must ensure that only the lower 48 bits get
* set. */
pub static mut XI: u64 = 0;
/* Multiplier and addend, which may be set through lcong48(). Default values as
* specified in POSIX. */
pub static mut A: u64 = 0x5deece66d;
pub static mut C: u16 = 0xb;
/// Advances the linear congruential generator to the next element in its
/// sequence.
pub unsafe fn generator_step() {
/* The recurrence relation of the linear congruential generator,
* X_(n+1) = (a * X_n + c) % m,
* with m = 2**48. The multiplication and addition can overflow a u64, but
* we just let it wrap since we take mod 2**48 anyway. */
XI = A.wrapping_mul(XI).wrapping_add(u64::from(C)) & 0xffff_ffff_ffff;
}
/// Get a C `double` from a 48-bit integer (for `drand48()` and `erand48()`).
pub fn x_to_float64(x: u64) -> c_double {
/* We set the exponent to 0, and the 48-bit integer is copied into the high
* 48 of the 52 significand bits. The value then lies in the range
* [1.0, 2.0), from which we simply subtract 1.0. */
f64::from_bits(0x3ff0_0000_0000_0000_u64 | (x << 4)) - 1.0f64
}
/// Get the high 31 bits of a 48-bit integer (for `lrand48()` and `nrand48()`).
pub fn x_to_uint31(x: u64) -> c_long {
(x >> 17) as c_long
}
/// Get the high 32 bits, signed, of a 48-bit integer (for `mrand48()` and
/// `jrand48()`).
pub fn x_to_int32(x: u64) -> c_long {
// Cast via i32 to ensure we get the sign correct
(x >> 16) as i32 as c_long
}
......@@ -20,6 +20,7 @@ use platform;
use platform::types::*;
use platform::{Pal, Sys};
mod lcg48;
mod sort;
pub const EXIT_FAILURE: c_int = 1;
......@@ -227,9 +228,10 @@ pub extern "C" fn div(numer: c_int, denom: c_int) -> div_t {
}
}
// #[no_mangle]
pub extern "C" fn drand48() -> c_double {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn drand48() -> c_double {
lcg48::generator_step();
lcg48::x_to_float64(lcg48::XI)
}
// #[no_mangle]
......@@ -410,9 +412,10 @@ pub extern "C" fn lldiv(numer: c_longlong, denom: c_longlong) -> lldiv_t {
}
}
// #[no_mangle]
pub extern "C" fn lrand48() -> c_long {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn lrand48() -> c_long {
lcg48::generator_step();
lcg48::x_to_uint31(lcg48::XI)
}
#[no_mangle]
......@@ -566,9 +569,10 @@ pub extern "C" fn mkstemps(name: *mut c_char, suffix_len: c_int) -> c_int {
mkostemps(name, suffix_len, 0)
}
// #[no_mangle]
pub extern "C" fn mrand48() -> c_long {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn mrand48() -> c_long {
lcg48::generator_step();
lcg48::x_to_int32(lcg48::XI)
}
// #[no_mangle]
......@@ -775,9 +779,12 @@ pub unsafe extern "C" fn srand(seed: c_uint) {
RNG = Some(XorShiftRng::from_seed([seed as u8; 16]));
}
// #[no_mangle]
pub extern "C" fn srand48(seed: c_long) {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn srand48(seedval: c_long) {
/* Set the high 32 bits of the 48-bit X_i value to the lower 32 bits
* of the input argument, and the lower 16 bits to 0x330e, as
* specified in POSIX. */
lcg48::XI = (((seedval & 0xffff_ffff) as u64) << 16) | 0x330e_u64;
}
// #[no_mangle]
......
......@@ -41,6 +41,7 @@ EXPECT_NAMES=\
stdlib/atoi \
stdlib/div \
stdlib/env \
stdlib/lcg48 \
stdlib/mkostemps \
stdlib/rand \
stdlib/strtod \
......
lrand48 (uninitialized): 0 2116118 89401895 379337186 782977366 196130996 198207689 1046291021 1131187612 975888346
drand48: 0.750266 0.607593 0.567593 0.799563 0.984984 0.205670 0.625922 0.794426 0.369416 0.854100
lrand48: 1611183183 1304796356 1218897288 1717049088 2115236938 441672110 1344158015 1706017430 793314380 1834165927
mrand48: -1072600929 -1685374584 -1857172720 -860869119 -64493420 883344220 -1606651266 -882932436 1586628760 -626635441
#include <stdlib.h>
#include <stdio.h>
#include "test_helpers.h"
int main(void) {
long x_l, x_m;
double x_d;
long seedval = 0xcafebeef;
printf("lrand48 (uninitialized):");
for (int i = 0; i < 10; i++)
{
x_l = lrand48();
printf(" %ld", x_l);
}
printf("\n");
srand48(seedval);
printf("drand48:");
for (int i = 0; i < 10; i++)
{
x_d = drand48();
printf(" %lf", x_d);
}
printf("\n");
srand48(seedval);
printf("lrand48:");
for (int i = 0; i < 10; i++)
{
x_l = lrand48();
printf(" %ld", x_l);
}
printf("\n");
srand48(seedval);
printf("mrand48:");
for (int i = 0; i < 10; i++)
{
x_m = mrand48();
printf(" %ld", x_m);
}
printf("\n");
}
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