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rand: fix edge case, when bit length is 31 and 63, add tests for rand.intn(2147483647)! etc (#18714)

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Subhomoy Haldar 2023-06-29 20:11:27 +01:00 committed by GitHub
parent cf323cd0ef
commit 7ab11097be
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2 changed files with 32 additions and 4 deletions
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16
vlib/rand/rand.v
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@ -55,7 +55,7 @@ pub fn (mut rng PRNG) u32n(max u32) !u32 {
// the closest power of two. Then we loop until we find
// an int in the required range
bit_len := bits.len_32(max)
if bit_len == 32 {
if _unlikely_(bit_len == 32) {
for {
value := rng.u32()
if value < max {
@ -63,7 +63,11 @@ pub fn (mut rng PRNG) u32n(max u32) !u32 {
}
}
} else {
mask := (u32(1) << (bit_len + 1)) - 1
mask := if _unlikely_(bit_len == 31) {
u32(0x7FFFFFFF)
} else {
(u32(1) << (bit_len + 1)) - 1
}
for {
value := rng.u32() & mask
if value < max {
@ -81,7 +85,7 @@ pub fn (mut rng PRNG) u64n(max u64) !u64 {
return error('max must be positive integer')
}
bit_len := bits.len_64(max)
if bit_len == 64 {
if _unlikely_(bit_len == 64) {
for {
value := rng.u64()
if value < max {
@ -89,7 +93,11 @@ pub fn (mut rng PRNG) u64n(max u64) !u64 {
}
}
} else {
mask := (u64(1) << (bit_len + 1)) - 1
mask := if _unlikely_(bit_len == 63) {
u64(0x7FFFFFFFFFFFFFFF)
} else {
(u64(1) << (bit_len + 1)) - 1
}
for {
value := rng.u64() & mask
if value < max {

20
vlib/rand/random_numbers_test.v
View File

@ -454,3 +454,23 @@ fn test_element2() {
assert 4 != e
}
}
fn test_proper_masking() {
under32 := []int{len: 10, init: index * 0 + rand.intn(1073741823)!}
assert under32 != [0].repeat(10)
over32 := []int{len: 10, init: index * 0 + rand.intn(1073741824)!}
assert over32 != [0].repeat(10)
under64 := []i64{len: 10, init: index * 0 + rand.i64n(i64(4611686018427387903))!}
assert under64 != [i64(0)].repeat(10)
over64 := []i64{len: 10, init: index * 0 + rand.i64n(i64(4611686018427387904))!}
assert over64 != [i64(0)].repeat(10)
almost_full32 := []int{len: 10, init: index * 0 + rand.intn(2147483647)!}
assert almost_full32 != [0].repeat(10)
almost_full64 := []i64{len: 10, init: index * 0 + rand.i64n(i64(9223372036854775807))!}
assert almost_full64 != [i64(0)].repeat(10)
}