From 45860e92565c115e395a96bf6042117c719c5b4b Mon Sep 17 00:00:00 2001
From: Peter Limkilde Svendsen <peter.limkilde@gmail.com>
Date: Sun, 12 May 2019 14:50:18 +0000
Subject: [PATCH] Implement LCG pseudorandom number functions
---
src/header/stdlib/lcg48.rs | 43 ++++++++++++++++++++++++++++
src/header/stdlib/mod.rs | 31 ++++++++++++--------
tests/Makefile | 1 +
tests/expected/stdlib/lcg48.stderr | 0
tests/expected/stdlib/lcg48.stdout | 4 +++
tests/stdlib/lcg48.c | 45 ++++++++++++++++++++++++++++++
6 files changed, 112 insertions(+), 12 deletions(-)
create mode 100644 src/header/stdlib/lcg48.rs
create mode 100644 tests/expected/stdlib/lcg48.stderr
create mode 100644 tests/expected/stdlib/lcg48.stdout
create mode 100644 tests/stdlib/lcg48.c
diff --git a/src/header/stdlib/lcg48.rs b/src/header/stdlib/lcg48.rs
new file mode 100644
index 000000000..cba8188ca
--- /dev/null
+++ b/src/header/stdlib/lcg48.rs
@@ -0,0 +1,43 @@
+//! 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
+}
diff --git a/src/header/stdlib/mod.rs b/src/header/stdlib/mod.rs
index 57ed49aa9..fb7457824 100644
--- a/src/header/stdlib/mod.rs
+++ b/src/header/stdlib/mod.rs
@@ -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]
diff --git a/tests/Makefile b/tests/Makefile
index c051b92e5..d4e0e9a40 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -41,6 +41,7 @@ EXPECT_NAMES=\
stdlib/atoi \
stdlib/div \
stdlib/env \
+ stdlib/lcg48 \
stdlib/mkostemps \
stdlib/rand \
stdlib/strtod \
diff --git a/tests/expected/stdlib/lcg48.stderr b/tests/expected/stdlib/lcg48.stderr
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/expected/stdlib/lcg48.stdout b/tests/expected/stdlib/lcg48.stdout
new file mode 100644
index 000000000..14522ff60
--- /dev/null
+++ b/tests/expected/stdlib/lcg48.stdout
@@ -0,0 +1,4 @@
+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
diff --git a/tests/stdlib/lcg48.c b/tests/stdlib/lcg48.c
new file mode 100644
index 000000000..da8c76a46
--- /dev/null
+++ b/tests/stdlib/lcg48.c
@@ -0,0 +1,45 @@
+#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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