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// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module rand
#include <sys/syscall.h>
const (
read_batch_size = 256
)
// read returns an array of `bytes_needed` random bytes read from the OS.
pub fn read(bytes_needed int) ?[]byte {
mut buffer := unsafe { malloc_noscan(bytes_needed) }
mut bytes_read := 0
mut remaining_bytes := bytes_needed
// getrandom syscall wont block if requesting <= 256 bytes
for bytes_read < bytes_needed {
batch_size := if remaining_bytes > rand.read_batch_size {
rand.read_batch_size
} else {
remaining_bytes
}
rbytes := unsafe { getrandom(batch_size, buffer + bytes_read) }
if rbytes == -1 {
unsafe { free(buffer) }
return IError(&ReadError{})
}
bytes_read += rbytes
}
return unsafe { buffer.vbytes(bytes_needed) }
}
fn getrandom(bytes_needed int, buffer voidptr) int {
if bytes_needed > rand.read_batch_size {
panic('getrandom() dont request more than $rand.read_batch_size bytes at once.')
}
return unsafe { C.syscall(C.SYS_getrandom, buffer, bytes_needed, 0) }
}
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