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fmt: use mem::uninitialized for float formatting buffers

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Spending time to initialize these is just wasted work, as we'll
overwrite them soon anyway.

Fixes #41259.
This commit is contained in:
Nathan Froyd 2017-04-14 16:25:49 -04:00
parent 2499d819d4
commit b2c3102e62
1 changed files with 34 additions and 22 deletions
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56
src/libcore/fmt/float.rs
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@ -9,6 +9,7 @@
// except according to those terms.
use fmt::{Formatter, Result, LowerExp, UpperExp, Display, Debug};
use mem;
use num::flt2dec;
// Don't inline this so callers don't use the stack space this function
@ -18,12 +19,14 @@ fn float_to_decimal_common_exact<T>(fmt: &mut Formatter, num: &T,
sign: flt2dec::Sign, precision: usize) -> Result
where T: flt2dec::DecodableFloat
{
let mut buf = [0; 1024]; // enough for f32 and f64
let mut parts = [flt2dec::Part::Zero(0); 5];
let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
false, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 5] = mem::uninitialized();
let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
false, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
}
}
// Don't inline this so callers that call both this and the above won't wind
@ -33,11 +36,14 @@ fn float_to_decimal_common_shortest<T>(fmt: &mut Formatter,
num: &T, sign: flt2dec::Sign) -> Result
where T: flt2dec::DecodableFloat
{
let mut buf = [0; flt2dec::MAX_SIG_DIGITS]; // enough for f32 and f64
let mut parts = [flt2dec::Part::Zero(0); 5];
let formatted = flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest,
*num, sign, 0, false, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
unsafe {
// enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
let mut parts: [flt2dec::Part; 5] = mem::uninitialized();
let formatted = flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest,
*num, sign, 0, false, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
}
}
// Common code of floating point Debug and Display.
@ -67,12 +73,14 @@ fn float_to_exponential_common_exact<T>(fmt: &mut Formatter, num: &T,
upper: bool) -> Result
where T: flt2dec::DecodableFloat
{
let mut buf = [0; 1024]; // enough for f32 and f64
let mut parts = [flt2dec::Part::Zero(0); 7];
let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
upper, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
unsafe {
let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
let mut parts: [flt2dec::Part; 7] = mem::uninitialized();
let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact,
*num, sign, precision,
upper, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
}
}
// Don't inline this so callers that call both this and the above won't wind
@ -83,11 +91,15 @@ fn float_to_exponential_common_shortest<T>(fmt: &mut Formatter,
upper: bool) -> Result
where T: flt2dec::DecodableFloat
{
let mut buf = [0; flt2dec::MAX_SIG_DIGITS]; // enough for f32 and f64
let mut parts = [flt2dec::Part::Zero(0); 7];
let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, *num,
sign, (0, 0), upper, &mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
unsafe {
// enough for f32 and f64
let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
let mut parts: [flt2dec::Part; 7] = mem::uninitialized();
let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest,
*num, sign, (0, 0), upper,
&mut buf, &mut parts);
fmt.pad_formatted_parts(&formatted)
}
}
// Common code of floating point LowerExp and UpperExp.