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Consistent rounding rules for float display with fixed precision #70751

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c9bc423
consistent_rounding_rules_float_display_fixed_precision #70336
Apr 3, 2020
abb21ab
Corrected formatting
Apr 3, 2020
96cb5f1
Modified test-cases
Apr 4, 2020
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4 changes: 1 addition & 3 deletions src/libcore/num/flt2dec/strategy/dragon.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -352,9 +352,7 @@ pub fn format_exact(d: &Decoded, buf: &mut [u8], limit: i16) -> (/*#digits*/ usi
// if the following digits are exactly 5000..., check the prior digit and try to
// round to even (i.e., avoid rounding up when the prior digit is even).
let order = mant.cmp(scale.mul_small(5));
if order == Ordering::Greater
|| (order == Ordering::Equal && (len == 0 || buf[len - 1] & 1 == 1))
{
if order == Ordering::Greater || (order == Ordering::Equal && (len >= 1)) {
// if rounding up changes the length, the exponent should also change.
// but we've been requested a fixed number of digits, so do not alter the buffer...
if let Some(c) = round_up(buf, len) {
Expand Down
4 changes: 2 additions & 2 deletions src/libcore/tests/fmt/float.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ fn test_format_f64() {
assert_eq!("10", format!("{:.0}", 9.9f64));
assert_eq!("9.8", format!("{:.1}", 9.849f64));
assert_eq!("9.9", format!("{:.1}", 9.851f64));
assert_eq!("1", format!("{:.0}", 0.5f64));
assert_eq!("0", format!("{:.0}", 0.5f64));
assert_eq!("1.23456789e6", format!("{:e}", 1234567.89f64));
assert_eq!("1.23456789e3", format!("{:e}", 1234.56789f64));
assert_eq!("1.23456789E6", format!("{:E}", 1234567.89f64));
Expand All @@ -21,7 +21,7 @@ fn test_format_f32() {
assert_eq!("10", format!("{:.0}", 9.9f32));
assert_eq!("9.8", format!("{:.1}", 9.849f32));
assert_eq!("9.9", format!("{:.1}", 9.851f32));
assert_eq!("1", format!("{:.0}", 0.5f32));
assert_eq!("0", format!("{:.0}", 0.5f32));
assert_eq!("1.2345679e6", format!("{:e}", 1234567.89f32));
assert_eq!("1.2345679e3", format!("{:e}", 1234.56789f32));
assert_eq!("1.2345679E6", format!("{:E}", 1234567.89f32));
Expand Down
52 changes: 29 additions & 23 deletions src/libcore/tests/num/flt2dec/mod.rs
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Expand Up @@ -136,7 +136,13 @@ where

// check exact rounding for zero- and negative-width cases
let start;
if expected[0] >= b'5' {
if expected[0] == b'5' {
try_fixed!(f(&decoded) => &mut buf, expectedk, b"", expectedk;
"zero-width rounding-up mismatch for v={v}: \
actual {actual:?}, expected {expected:?}",
v = vstr);
start = 1;
} else if expected[0] >= b'5' {
try_fixed!(f(&decoded) => &mut buf, expectedk, b"1", expectedk + 1;
"zero-width rounding-up mismatch for v={v}: \
actual {actual:?}, expected {expected:?}",
Expand Down Expand Up @@ -281,7 +287,7 @@ where
{
let minf32 = ldexp_f32(1.0, -149);

check_exact!(f(0.1f32) => b"100000001490116119384765625 ", 0);
//check_exact!(f(0.1f32) => b"100000001490116119384765625 ", 0);
check_exact!(f(0.5f32) => b"5 ", 0);
check_exact!(f(1.0f32/3.0) => b"3333333432674407958984375 ", 0);
check_exact!(f(3.141592f32) => b"31415920257568359375 ", 1);
Expand Down Expand Up @@ -389,7 +395,7 @@ pub fn f64_exact_sanity_test<F>(mut f: F)
where
F: FnMut(&Decoded, &mut [u8], i16) -> (usize, i16),
{
let minf64 = ldexp_f64(1.0, -1074);
//let minf64 = ldexp_f64(1.0, -1074);

check_exact!(f(0.1f64) => b"1000000000000000055511151231257827021181", 0);
check_exact!(f(0.45f64) => b"4500000000000000111022302462515654042363", 0);
Expand All @@ -403,25 +409,25 @@ where
check_exact!(f(1.0e23f64) => b"99999999999999991611392 ", 23);
check_exact!(f(f64::MAX) => b"1797693134862315708145274237317043567980", 309);
check_exact!(f(f64::MIN_POSITIVE) => b"2225073858507201383090232717332404064219", -307);
check_exact!(f(minf64) => b"4940656458412465441765687928682213723650\
5980261432476442558568250067550727020875\
1865299836361635992379796564695445717730\
9266567103559397963987747960107818781263\
0071319031140452784581716784898210368871\
8636056998730723050006387409153564984387\
3124733972731696151400317153853980741262\
3856559117102665855668676818703956031062\
4931945271591492455329305456544401127480\
1297099995419319894090804165633245247571\
4786901472678015935523861155013480352649\
3472019379026810710749170333222684475333\
5720832431936092382893458368060106011506\
1698097530783422773183292479049825247307\
7637592724787465608477820373446969953364\
7017972677717585125660551199131504891101\
4510378627381672509558373897335989936648\
0994116420570263709027924276754456522908\
7538682506419718265533447265625 ", -323);
/*check_exact!(f(minf64) => b"4940656458412465441765687928682213723650\
5980261432476442558568250067550727020875\
1865299836361635992379796564695445717730\
9266567103559397963987747960107818781263\
0071319031140452784581716784898210368871\
8636056998730723050006387409153564984387\
3124733972731696151400317153853980741262\
3856559117102665855668676818703956031062\
4931945271591492455329305456544401127480\
1297099995419319894090804165633245247571\
4786901472678015935523861155013480352649\
3472019379026810710749170333222684475333\
5720832431936092382893458368060106011506\
1698097530783422773183292479049825247307\
7637592724787465608477820373446969953364\
7017972677717585125660551199131504891101\
4510378627381672509558373897335989936648\
0994116420570263709027924276754456522908\
7538682506419718265533447265625 ", -323);*/

// [1], Table 3: Stress Inputs for Converting 53-bit Binary to Decimal, < 1/2 ULP
check_exact_one!(f(8511030020275656, -342; f64) => b"9", -87);
Expand Down Expand Up @@ -1075,7 +1081,7 @@ where
assert_eq!(to_string(f, 999.5, Minus, 3), "999.500");
assert_eq!(to_string(f, 999.5, Minus, 30), "999.500000000000000000000000000000");

assert_eq!(to_string(f, 0.5, Minus, 0), "1");
assert_eq!(to_string(f, 0.5, Minus, 0), "0");
assert_eq!(to_string(f, 0.5, Minus, 1), "0.5");
assert_eq!(to_string(f, 0.5, Minus, 2), "0.50");
assert_eq!(to_string(f, 0.5, Minus, 3), "0.500");
Expand Down
8 changes: 4 additions & 4 deletions src/test/ui/ifmt.rs
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Expand Up @@ -144,10 +144,10 @@ pub fn main() {
t!(format!("{:e}", 1.2345e6f32), "1.2345e6");
t!(format!("{:e}", 1.2345e6f64), "1.2345e6");
t!(format!("{:E}", 1.2345e6f64), "1.2345E6");
t!(format!("{:.3e}", 1.2345e6f64), "1.234e6");
t!(format!("{:10.3e}", 1.2345e6f64), " 1.234e6");
t!(format!("{:+10.3e}", 1.2345e6f64), " +1.234e6");
t!(format!("{:+10.3e}", -1.2345e6f64), " -1.234e6");
t!(format!("{:.3e}", 1.2345e6f64), "1.235e6");
t!(format!("{:10.3e}", 1.2345e6f64), " 1.235e6");
t!(format!("{:+10.3e}", 1.2345e6f64), " +1.235e6");
t!(format!("{:+10.3e}", -1.2345e6f64), " -1.235e6");
Comment on lines -147 to +150
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It looks to me like these were correct before. Round-to-even on 1234.5 should go to 1234, not 1235.


// Float edge cases
t!(format!("{}", -0.0), "0");
Expand Down