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Merge branch 'lcg48_arr' into 'master'

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Implement remaining LCG functions

See merge request redox-os/relibc!219
This commit is contained in:
jD91mZM2
2019-06-12 09:31:18 +00:00
parent 3013c5db50 7a48107080
commit d9ed51b9f1
4 changed files with 218 additions and 53 deletions
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src/header/stdlib/lcg48.rs
+68 -25
View File
@@ -1,43 +1,86 @@
//! Helper functions for pseudorandom number generation using LCG, see http://pubs.opengroup.org/onlinepubs/7908799/xsh/drand48.html
//! Helper functions for pseudorandom number generation using LCG, see https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/functions/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;
/* The default element buffer for the linear congruential generator's
* sequence. Implemented using a c_ushort array for consistency between
* the drand48()/lrand48()/mrand48() and erand48()/nrand48()/jrand48()
* functions, and with STASHED_XI (see below). */
pub static mut DEFAULT_XI: [c_ushort; 3] = [0; 3];
/* 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;
// Used by seed48() (returns a pointer to this array).
pub static mut STASHED_XI: [c_ushort; 3] = [0; 3];
/// 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;
/* Multiplier and addend, which may be set through lcong48(). Default
* values as specified in POSIX. */
const A_DEFAULT_VALUE: u64 = 0x5deece66d;
const C_DEFAULT_VALUE: u16 = 0xb;
pub static mut A: u64 = A_DEFAULT_VALUE;
pub static mut C: u16 = C_DEFAULT_VALUE;
/// Used by `srand48()` and `seed48()`.
pub unsafe fn reset_a_and_c() {
A = A_DEFAULT_VALUE;
C = C_DEFAULT_VALUE;
}
/// Get a C `double` from a 48-bit integer (for `drand48()` and `erand48()`).
pub fn x_to_float64(x: u64) -> c_double {
/// Build a 48-bit integer from a size-3 array of unsigned short.
///
/// Takes a pointer argument due to the inappropriate C function
/// signatures generated from Rust's sized arrays, see
/// https://github.com/eqrion/cbindgen/issues/171
pub unsafe fn uint48_from_ushort_arr3(arr_ptr: *const c_ushort) -> u64 {
let arr = [*arr_ptr.offset(0), *arr_ptr.offset(1), *arr_ptr.offset(2)];
/* Cast via u16 to ensure we get only the lower 16 bits of each
* element, as specified by POSIX. */
u64::from(arr[0] as u16) | (u64::from(arr[1] as u16) << 16) | (u64::from(arr[2] as u16) << 32)
}
/// Set a size-3 array of unsigned short from a 48-bit integer.
pub unsafe fn set_ushort_arr3_from_uint48(arr_ptr: *mut c_ushort, value: u64) {
*arr_ptr.offset(0) = c_ushort::from(value as u16);
*arr_ptr.offset(1) = c_ushort::from((value >> 16) as u16);
*arr_ptr.offset(2) = c_ushort::from((value >> 32) as u16);
}
/// Advances the buffer from the input argument to the next element in
/// the linear congruential generator's sequence.
///
/// Modifies the passed argument in-place and returns the new value as a
/// u64. The input argument must be a size-3 array.
pub unsafe fn generator_step(xi_arr_ptr: *mut c_ushort) -> u64 {
let old_xi: u64 = uint48_from_ushort_arr3(xi_arr_ptr);
/* 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. */
let new_xi: u64 = A.wrapping_mul(old_xi).wrapping_add(u64::from(C)) & 0xffff_ffff_ffff;
set_ushort_arr3_from_uint48(xi_arr_ptr, new_xi);
new_xi
}
/// Get a C `double` from a 48-bit integer (for `drand48()` and
/// `erand48()`).
pub fn float64_from_x(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 {
/// Get the high 31 bits of a 48-bit integer (for `lrand48()` and
/// `nrand48()`).
pub fn uint31_from_x(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 {
/// Get the high 32 bits, signed, of a 48-bit integer (for `mrand48()`
/// and `jrand48()`).
pub fn int32_from_x(x: u64) -> c_long {
// Cast via i32 to ensure we get the sign correct
(x >> 16) as i32 as c_long
c_long::from((x >> 16) as i32)
}
src/header/stdlib/mod.rs
+42 -22
View File
@@ -232,8 +232,8 @@ pub extern "C" fn div(numer: c_int, denom: c_int) -> div_t {
#[no_mangle]
pub unsafe extern "C" fn drand48() -> c_double {
lcg48::generator_step();
lcg48::x_to_float64(lcg48::XI)
let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
lcg48::float64_from_x(new_xi)
}
// #[no_mangle]
@@ -246,9 +246,10 @@ pub extern "C" fn ecvt(
unimplemented!();
}
// #[no_mangle]
pub extern "C" fn erand(xsubi: [c_ushort; 3]) -> c_double {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn erand48(xsubi: *mut c_ushort) -> c_double {
let new_xi = lcg48::generator_step(xsubi);
lcg48::float64_from_x(new_xi)
}
#[no_mangle]
@@ -361,9 +362,10 @@ pub extern "C" fn initstate(seec: c_uint, state: *mut c_char, size: size_t) -> *
unimplemented!();
}
// #[no_mangle]
pub extern "C" fn jrand48(xsubi: [c_ushort; 3]) -> c_long {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn jrand48(xsubi: *mut c_ushort) -> c_long {
let new_xi = lcg48::generator_step(xsubi);
lcg48::int32_from_x(new_xi)
}
// #[no_mangle]
@@ -376,9 +378,16 @@ pub extern "C" fn labs(i: c_long) -> c_long {
i.abs()
}
// #[no_mangle]
pub extern "C" fn lcong48(param: [c_ushort; 7]) {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn lcong48(param: *mut c_ushort) {
// Input should be a size-7 array.
/* Go through this ptr -> u64 -> ptr conversion to ensure we only
* get the lower 16 bits of each element. */
let new_xi = lcg48::uint48_from_ushort_arr3(param.offset(0));
lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
lcg48::A = lcg48::uint48_from_ushort_arr3(param.offset(3));
lcg48::C = *param.offset(6) as u16; // c_ushort may be more than 16 bits
}
#[repr(C)]
@@ -416,8 +425,8 @@ pub extern "C" fn lldiv(numer: c_longlong, denom: c_longlong) -> lldiv_t {
#[no_mangle]
pub unsafe extern "C" fn lrand48() -> c_long {
lcg48::generator_step();
lcg48::x_to_uint31(lcg48::XI)
let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
lcg48::uint31_from_x(new_xi)
}
#[no_mangle]
@@ -573,13 +582,14 @@ pub extern "C" fn mkstemps(name: *mut c_char, suffix_len: c_int) -> c_int {
#[no_mangle]
pub unsafe extern "C" fn mrand48() -> c_long {
lcg48::generator_step();
lcg48::x_to_int32(lcg48::XI)
let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
lcg48::int32_from_x(new_xi)
}
// #[no_mangle]
pub extern "C" fn nrand48(xsubi: [c_ushort; 3]) -> c_long {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn nrand48(xsubi: *mut c_ushort) -> c_long {
let new_xi = lcg48::generator_step(xsubi);
lcg48::uint31_from_x(new_xi)
}
#[no_mangle]
@@ -719,9 +729,16 @@ pub unsafe extern "C" fn realpath(pathname: *const c_char, resolved: *mut c_char
ptr
}
// #[no_mangle]
pub extern "C" fn seed48(seed16v: [c_ushort; 3]) -> c_ushort {
unimplemented!();
#[no_mangle]
pub unsafe extern "C" fn seed48(seed16v: *mut c_ushort) -> *mut c_ushort {
lcg48::reset_a_and_c();
lcg48::STASHED_XI = lcg48::DEFAULT_XI;
let new_xi = lcg48::uint48_from_ushort_arr3(seed16v);
lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
lcg48::STASHED_XI.as_mut_ptr()
}
#[no_mangle]
@@ -808,10 +825,13 @@ pub unsafe extern "C" fn srand(seed: c_uint) {
#[no_mangle]
pub unsafe extern "C" fn srand48(seedval: c_long) {
lcg48::reset_a_and_c();
/* 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;
let new_xi = (((seedval as u32) as u64) << 16) | 0x330e_u64;
lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
}
// #[no_mangle]