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auto merge of #5769 : gifnksm/rust/range_step, r=bstrie

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`uint::range_step` or `int::range_step` causes overflow or underflow as following.
code:
```rust
fn main() {
    for uint::range_step(3, 0, -2) |n| {
        println(fmt!("%u", n));
    }
}
```
output:
```
3
1
18446744073709551615
18446744073709551613
...
```
This commit fixes this behavior as follows.
```
3
1
```
This commit is contained in:
bors 2013-04-09 07:52:04 -07:00
commit 412a07055c
2 changed files with 49 additions and 10 deletions
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28
src/libcore/num/int-template.rs
View file

@ -107,11 +107,15 @@ pub fn range_step(start: T, stop: T, step: T, it: &fn(T) -> bool) {
} else if step > 0 { // ascending
while i < stop {
if !it(i) { break }
// avoiding overflow. break if i + step > max_value
if i > max_value - step { break; }
i += step;
}
} else { // descending
while i > stop {
if !it(i) { break }
// avoiding underflow. break if i + step < min_value
if i < min_value - step { break; }
i += step;
}
}
@ -421,10 +425,26 @@ pub fn test_ranges() {
for range_step(36,30,-2) |i| {
l.push(i);
}
assert!(l == ~[0,1,2,
13,12,11,
20,22,24,
36,34,32]);
for range_step(max_value - 2, max_value, 2) |i| {
l.push(i);
}
for range_step(max_value - 3, max_value, 2) |i| {
l.push(i);
}
for range_step(min_value + 2, min_value, -2) |i| {
l.push(i);
}
for range_step(min_value + 3, min_value, -2) |i| {
l.push(i);
}
assert_eq!(l, ~[0,1,2,
13,12,11,
20,22,24,
36,34,32,
max_value-2,
max_value-3,max_value-1,
min_value+2,
min_value+3,min_value+1]);
// None of the `fail`s should execute.
for range(10,0) |_i| {

31
src/libcore/num/uint-template.rs
View file

@ -78,12 +78,15 @@ pub fn range_step(start: T,
if step >= 0 {
while i < stop {
if !it(i) { break }
// avoiding overflow. break if i + step > max_value
if i > max_value - (step as T) { break; }
i += step as T;
}
}
else {
} else {
while i > stop {
if !it(i) { break }
// avoiding underflow. break if i + step < min_value
if i < min_value + ((-step) as T) { break; }
i -= -step as T;
}
}
@ -371,11 +374,27 @@ pub fn test_ranges() {
for range_step(36,30,-2) |i| {
l.push(i);
}
for range_step(max_value - 2, max_value, 2) |i| {
l.push(i);
}
for range_step(max_value - 3, max_value, 2) |i| {
l.push(i);
}
for range_step(min_value + 2, min_value, -2) |i| {
l.push(i);
}
for range_step(min_value + 3, min_value, -2) |i| {
l.push(i);
}
assert!(l == ~[0,1,2,
13,12,11,
20,22,24,
36,34,32]);
assert_eq!(l, ~[0,1,2,
13,12,11,
20,22,24,
36,34,32,
max_value-2,
max_value-3,max_value-1,
min_value+2,
min_value+3,min_value+1]);
// None of the `fail`s should execute.
for range(0,0) |_i| {