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use rand_core::RngCore;
#[derive(Debug)]
pub struct RepeatSeqFakeRng {
cnt: usize,
seq: Vec<u64>,
}
impl RepeatSeqFakeRng {
pub fn new(seq: Vec<u64>) -> Self {
assert_ne!(seq.len(), 0, "seq.len() > 0 is required.");
Self { cnt: 0, seq }
}
}
impl RngCore for RepeatSeqFakeRng {
fn next_u32(&mut self) -> u32 {
self.next_u64() as u32
}
fn next_u64(&mut self) -> u64 {
let i = self.cnt;
self.cnt += 1;
match self.seq.get(i) {
Some(x) => *x,
None => {
self.cnt = 1;
self.seq[0]
}
}
}
fn fill_bytes(&mut self, dest: &mut [u8]){
let mut ofs = 0;
while ofs + 8 <= dest.len() {
let v = self.next_u64();
dest[ofs] = (v & 0xff) as u8;
dest[ofs + 1] = ((v & 0xff00) >> 8) as u8;
dest[ofs + 2] = ((v & 0xff0000) >> 16) as u8;
dest[ofs + 3] = ((v & 0xff000000) >> 24) as u8;
dest[ofs + 4] = ((v & 0xff00000000) >> 32) as u8;
dest[ofs + 5] = ((v & 0xff0000000000) >> 40) as u8;
dest[ofs + 6] = ((v & 0xff000000000000) >> 48) as u8;
dest[ofs + 7] = ((v & 0xff00000000000000) >> 56) as u8;
ofs += 8;
}
let mut v = self.next_u64();
while ofs < dest.len() {
dest[ofs] = (v & 0xff) as u8;
v = v >> 8;
ofs += 1;
}
}
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
Ok(self.fill_bytes(dest))
}
}
#[cfg(test)]
mod tests {
use crate::RepeatSeqFakeRng;
use rand_core::RngCore;
#[test]
fn test_u64() {
let mut rng = RepeatSeqFakeRng::new(vec![100, 200, 300]);
assert_eq!(rng.next_u64(), 100);
assert_eq!(rng.next_u64(), 200);
assert_eq!(rng.next_u64(), 300);
assert_eq!(rng.next_u64(), 100);
assert_eq!(rng.next_u64(), 200);
assert_eq!(rng.next_u64(), 300);
assert_eq!(rng.next_u64(), 100);
}
#[test]
fn test_u32() {
let mut rng = RepeatSeqFakeRng::new(vec![(100 << 32) | 5, (200 << 32) | 6, (300 << 32) | 7]);
assert_eq!(rng.next_u32(), 5);
assert_eq!(rng.next_u32(), 6);
assert_eq!(rng.next_u32(), 7);
}
#[test]
fn test_len1() {
let mut rng = RepeatSeqFakeRng::new(vec![1]);
assert_eq!(rng.next_u64(), 1);
assert_eq!(rng.next_u32(), 1);
assert_eq!(rng.next_u64(), 1);
}
#[test]
fn fill_bytes_justsize() {
let mut rng = RepeatSeqFakeRng::new(vec![0x4142434445464748, 0x494a4b4c4d4e4f50]);
let mut vec = vec![0; 16];
rng.fill_bytes(vec.as_mut());
assert_eq!(vec.as_slice(), b"HGFEDCBAPONMLKJI");
}
#[test]
fn fill_bytes_repeated() {
let mut rng = RepeatSeqFakeRng::new(vec![0x4142434445464748, 0x494a4b4c4d4e4f50]);
let mut vec = vec![0; 16];
let _ = rng.next_u64();
rng.fill_bytes(vec.as_mut());
assert_eq!(vec.as_slice(), b"PONMLKJIHGFEDCBA");
}
#[test]
fn fill_bytes_smallsize() {
let mut rng = RepeatSeqFakeRng::new(vec![0x4142434445464748, 0x494a4b4c4d4e4f50, 0xdeadbeef]);
let mut vec = vec![0; 3];
let _ = rng.next_u64();
rng.fill_bytes(vec.as_mut());
assert_eq!(vec.as_slice(), b"PON");
assert_eq!(rng.next_u64(), 0xdeadbeef);
}
}