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flt2dec: properly handle uninitialized memory #76241

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Sep 2, 2020
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flt2dec: properly handle uninitialized memory #76241

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49 changes: 33 additions & 16 deletions library/core/benches/num/flt2dec/strategy/dragon.rs
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,59 +1,76 @@
use super::super::*;
use core::num::flt2dec::strategy::dragon::*;
use std::mem::MaybeUninit;
use test::Bencher;

#[bench]
fn bench_small_shortest(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; MAX_SIG_DIGITS];
b.iter(|| format_shortest(&decoded, &mut buf));
let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
b.iter(|| {
format_shortest(&decoded, &mut buf);
});
}

#[bench]
fn bench_big_shortest(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; MAX_SIG_DIGITS];
b.iter(|| format_shortest(&decoded, &mut buf));
let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
b.iter(|| {
format_shortest(&decoded, &mut buf);
});
}

#[bench]
fn bench_small_exact_3(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 3];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 3];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_3(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 3];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 3];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_small_exact_12(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 12];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 12];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_12(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 12];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 12];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_small_exact_inf(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 1024];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 1024];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_inf(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 1024];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 1024];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}
49 changes: 33 additions & 16 deletions library/core/benches/num/flt2dec/strategy/grisu.rs
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
use super::super::*;
use core::num::flt2dec::strategy::grisu::*;
use std::mem::MaybeUninit;
use test::Bencher;

pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
Expand All @@ -12,55 +13,71 @@ pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
#[bench]
fn bench_small_shortest(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; MAX_SIG_DIGITS];
b.iter(|| format_shortest(&decoded, &mut buf));
let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
b.iter(|| {
format_shortest(&decoded, &mut buf);
});
}

#[bench]
fn bench_big_shortest(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; MAX_SIG_DIGITS];
b.iter(|| format_shortest(&decoded, &mut buf));
let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
b.iter(|| {
format_shortest(&decoded, &mut buf);
});
}

#[bench]
fn bench_small_exact_3(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 3];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 3];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_3(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 3];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 3];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_small_exact_12(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 12];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 12];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_12(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 12];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 12];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_small_exact_inf(b: &mut Bencher) {
let decoded = decode_finite(3.141592f64);
let mut buf = [0; 1024];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 1024];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}

#[bench]
fn bench_big_exact_inf(b: &mut Bencher) {
let decoded = decode_finite(f64::MAX);
let mut buf = [0; 1024];
b.iter(|| format_exact(&decoded, &mut buf, i16::MIN));
let mut buf = [MaybeUninit::new(0); 1024];
b.iter(|| {
format_exact(&decoded, &mut buf, i16::MIN);
});
}
116 changes: 48 additions & 68 deletions library/core/src/fmt/float.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,25 +14,17 @@ fn float_to_decimal_common_exact<T>(
where
T: flt2dec::DecodableFloat,
{
// SAFETY: Possible undefined behavior, see FIXME(#76092)
unsafe {
let mut buf = MaybeUninit::<[u8; 1024]>::uninit(); // enough for f32 and f64
let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 4]>::uninit();
// FIXME(#76092): This is calling `assume_init_mut` on an uninitialized
// `MaybeUninit` (here and elsewhere in this file). Revisit this once
// we decided whether that is valid or not.
// We can do this only because we are libstd and coupled to the compiler.
// (FWIW, using `freeze` would not be enough; `flt2dec::Part` is an enum!)
let formatted = flt2dec::to_exact_fixed_str(
flt2dec::strategy::grisu::format_exact,
*num,
sign,
precision,
buf.assume_init_mut(),
parts.assume_init_mut(),
);
fmt.pad_formatted_parts(&formatted)
}
let mut buf: [MaybeUninit<u8>; 1024] = MaybeUninit::uninit_array(); // enough for f32 and f64
let mut parts: [MaybeUninit<flt2dec::Part<'_>>; 4] = MaybeUninit::uninit_array();
let formatted = flt2dec::to_exact_fixed_str(
flt2dec::strategy::grisu::format_exact,
*num,
sign,
precision,
&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
Expand All @@ -47,22 +39,18 @@ fn float_to_decimal_common_shortest<T>(
where
T: flt2dec::DecodableFloat,
{
// SAFETY: Possible undefined behavior, see FIXME(#76092)
unsafe {
// enough for f32 and f64
let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninit();
let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 4]>::uninit();
// FIXME(#76092)
let formatted = flt2dec::to_shortest_str(
flt2dec::strategy::grisu::format_shortest,
*num,
sign,
precision,
buf.assume_init_mut(),
parts.assume_init_mut(),
);
fmt.pad_formatted_parts(&formatted)
}
// enough for f32 and f64
let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] = MaybeUninit::uninit_array();
let mut parts: [MaybeUninit<flt2dec::Part<'_>>; 4] = MaybeUninit::uninit_array();
let formatted = flt2dec::to_shortest_str(
flt2dec::strategy::grisu::format_shortest,
*num,
sign,
precision,
&mut buf,
&mut parts,
);
fmt.pad_formatted_parts(&formatted)
}

// Common code of floating point Debug and Display.
Expand Down Expand Up @@ -103,22 +91,18 @@ fn float_to_exponential_common_exact<T>(
where
T: flt2dec::DecodableFloat,
{
// SAFETY: Possible undefined behavior, see FIXME(#76092)
unsafe {
let mut buf = MaybeUninit::<[u8; 1024]>::uninit(); // enough for f32 and f64
let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 6]>::uninit();
// FIXME(#76092)
let formatted = flt2dec::to_exact_exp_str(
flt2dec::strategy::grisu::format_exact,
*num,
sign,
precision,
upper,
buf.assume_init_mut(),
parts.assume_init_mut(),
);
fmt.pad_formatted_parts(&formatted)
}
let mut buf: [MaybeUninit<u8>; 1024] = MaybeUninit::uninit_array(); // enough for f32 and f64
let mut parts: [MaybeUninit<flt2dec::Part<'_>>; 6] = MaybeUninit::uninit_array();
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
Expand All @@ -133,23 +117,19 @@ fn float_to_exponential_common_shortest<T>(
where
T: flt2dec::DecodableFloat,
{
// SAFETY: Possible undefined behavior, see FIXME(#76092)
unsafe {
// enough for f32 and f64
let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninit();
let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 6]>::uninit();
// FIXME(#76092)
let formatted = flt2dec::to_shortest_exp_str(
flt2dec::strategy::grisu::format_shortest,
*num,
sign,
(0, 0),
upper,
buf.assume_init_mut(),
parts.assume_init_mut(),
);
fmt.pad_formatted_parts(&formatted)
}
// enough for f32 and f64
let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] = MaybeUninit::uninit_array();
let mut parts: [MaybeUninit<flt2dec::Part<'_>>; 6] = MaybeUninit::uninit_array();
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.
Expand Down
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