This commit globally defines the `Z_LIBC_DATA` macro, which is used to
place variables into the libc memory partition, so that it can be
re-used.
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
This commit introduces a new configuration called
`CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS`, which enables the
traditional non-reentrant (i.e. not thread-safe) version of the C
standard library functions such as rand() and gmtime() when the
respective configs are enabled.
The non-reentrant functions make use of the globals and require an
additional memory partition (MPU region), which is scarce on low-end
devices, when CONFIG_USERSPACE=y.
The purpose of this option is to classify the MPU resource intensive
functions as a separate category and only enable them when there is a
demand for such.
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
This commit adds the `rand_r` function, which is a reentrant (i.e.
thread-safe) version of the `rand` function, such that a thread-safe
variant is always available.
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
In order to bring consistency in-tree, migrate all lib code to the new
prefix <zephyr/...>. Note that the conversion has been scripted, refer
to zephyrproject-rtos#45388 for more details.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
rand() and srand() are pseudo-random number generator functions
defined in ISO C. This implementation uses the Linear Congruential
Generator (LCG) algorithm with the following parameters, which are the
same as used in GNU Libc "TYPE_0" algorithm.
Modulus 2^31
Multiplier 1103515245
Increment 12345
Output Bits 30..0
Note that the default algorithm used by GNU Libc is not TYPE_0, and
TYPE_0 should be selected first by an initstate() call as shown below.
All global variables in a C library must be routed to a memory
partition in order to be used by user-mode applications when
CONFIG_USERSPACE is enabled. Thus, srand_seed is marked as
such. z_libc_partition is originally used by the Newlib C library but
it's generic enough to be used by either the minimal libc or the
newlib.
All other functions in the Minimal C library, however, don't require
global variables/states. Unconditionally using z_libc_partition with
the minimal libc might be a problem for applications utilizing many
custom memory partitions on platforms with a limited number of MPU
regions (eg. Cortex M0/M3). This commit introduces a kconfig option
CONFIG_MINIMAL_LIBC_RAND so that applications can enable the
functions if needed. The option is disabled by default.
Because this commit _does_ implement rand() and srand(), our coding
guideline check on GitHub Action finds it as a violation.
Error: lib/libc/minimal/include/stdlib.h:45:WARNING: Violation to
rule 21.2 (Should not used a reserved identifier) - srand
But this is false positive.
The following is a simple test program for LCG with GNU Libc.
#include <stdio.h>
#include <stdlib.h>
int main()
{
static char state[8];
/* Switch GLIBC to use LCG/TYPE_0 generator type. */
initstate(0, state, sizeof(state));
srand(1); /* Or any other value. */
printf("%d\n", rand());
printf("%d\n", rand());
return 0;
}
See initstate(3p) for more detail about how to use LCG in GLIBC.
Signed-off-by: Yasushi SHOJI <yashi@spacecubics.com>
