GIS Library - Pseudo-random number generation. More...
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>#include <grass/gis.h>#include <grass/glocale.h>#include <sys/time.h>#include <sys/types.h>#include <unistd.h>
Go to the source code of this file.
Macros | |
| #define | LRAND48_ATOMIC 0 |
| #define | LO(x) ((x) & 0xFFFFU) |
| #define | HI(x) ((x) >> 16) |
Typedefs | |
| typedef unsigned short | uint16 |
| typedef unsigned int | uint32 |
| typedef signed int | int32 |
Functions | |
| void | G_srand48 (long seedval) |
| Seed the pseudo-random number generator. | |
| long | G_srand48_auto (void) |
| Seed the pseudo-random number generator from the time and PID. | |
| long | G_lrand48 (void) |
| Generate an integer in the range [0, 2^31) | |
| long | G_mrand48 (void) |
| Generate an integer in the range [-2^31, 2^31) | |
| double | G_drand48 (void) |
| Generate a floating-point value in the range [0,1) | |
Detailed Description
GIS Library - Pseudo-random number generation.
The generator is the standard drand48 linear congruential generator X' = (A * X + B) mod 2^48 with A = 0x5DEECE66D and B = 0xB.
When C11 atomic operations are available, the generator state is advanced with an atomic compare-and-swap and the generating functions are thread-safe: the sequence of generated values for a given seed is the same as in a single-threaded run. Which thread receives which value depends on scheduling, so results are fully reproducible only with single-threaded execution. Without C11 atomics (notably MSVC, which defines STDC_NO_ATOMICS), the generator falls back to plain state updates, so multi-threaded usage is safe only when compiled with C11 atomics.
The seeding functions are not thread-safe; see G_srand48().
SPDX-FileCopyrightText: 2014-2026 GRASS Development Team SPDX-License-Identifier: GPL-2.0-or-later
Definition in file lrand48.c.
Macro Definition Documentation
◆ HI
◆ LO
◆ LRAND48_ATOMIC
Typedef Documentation
◆ int32
◆ uint16
◆ uint32
Function Documentation
◆ G_drand48()
Generate a floating-point value in the range [0,1)
This function is thread-safe only when compiled with C11 atomics (see the comment at the top of the file).
- Returns
- the generated value
Definition at line 256 of file lrand48.c.
References r.
Referenced by f_rand(), and G_math_rand().
◆ G_lrand48()
Generate an integer in the range [0, 2^31)
This function is thread-safe only when compiled with C11 atomics (see the comment at the top of the file).
- Returns
- the generated value
Definition at line 212 of file lrand48.c.
References r.
Referenced by Rast_make_random_colors().
◆ G_mrand48()
◆ G_srand48()
Seed the pseudo-random number generator.
This function is not thread-safe. In a multi-threaded program, call G_srand48() once before starting the worker threads; it must not run concurrently with another thread seeding or generating values.
- Parameters
-
[in] seedval 32-bit integer used to seed the PRNG
Definition at line 95 of file lrand48.c.
References HI, LO, state, and x.
Referenced by G_math_srand(), and G_srand48_auto().
◆ G_srand48_auto()
Seed the pseudo-random number generator from the time and PID.
A weak hash of the current time and PID is generated and used to seed the PRNG
This function is not thread-safe. In a multi-threaded program, call G_srand48_auto() once before starting the worker threads; it must not run concurrently with another thread seeding or generating values.
- Returns
- generated seed value passed to G_srand48()
Definition at line 121 of file lrand48.c.
References _, AMI_STREAM< T >::AMI_STREAM(), G_fatal_error(), G_srand48(), getpid, gettimeofday(), NULL, and t.
Referenced by G_math_srand_auto(), and Rast_make_random_colors().
