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Use SmallVec to avoid allocations in from_decimal_string. #55816

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Nov 11, 2018
+10 −6
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Use SmallVec to avoid allocations in from_decimal_string. #55816

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1 change: 1 addition & 0 deletions src/Cargo.lock
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Expand Up @@ -2095,6 +2095,7 @@ version = "0.0.0"
dependencies = [
"bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
"rustc_cratesio_shim 0.0.0",
"smallvec 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
]

[[package]]
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1 change: 1 addition & 0 deletions src/librustc_apfloat/Cargo.toml
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Expand Up @@ -10,3 +10,4 @@ path = "lib.rs"
[dependencies]
bitflags = "1.0"
rustc_cratesio_shim = { path = "../librustc_cratesio_shim" }
smallvec = { version = "0.6.5", features = ["union"] }
13 changes: 7 additions & 6 deletions src/librustc_apfloat/ieee.rs
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Expand Up @@ -11,6 +11,7 @@
use {Category, ExpInt, IEK_INF, IEK_NAN, IEK_ZERO};
use {Float, FloatConvert, ParseError, Round, Status, StatusAnd};

use smallvec::{SmallVec, smallvec};
use std::cmp::{self, Ordering};
use std::convert::TryFrom;
use std::fmt::{self, Write};
Expand Down Expand Up @@ -1962,7 +1963,7 @@ impl<S: Semantics> IeeeFloat<S> {
// to hold the full significand, and an extra limb required by
// tcMultiplyPart.
let max_limbs = limbs_for_bits(1 + 196 * significand_digits / 59);
let mut dec_sig = Vec::with_capacity(max_limbs);
let mut dec_sig: SmallVec<[Limb; 1]> = SmallVec::with_capacity(max_limbs);

// Convert to binary efficiently - we do almost all multiplication
// in a Limb. When this would overflow do we do a single
Expand Down Expand Up @@ -2021,11 +2022,11 @@ impl<S: Semantics> IeeeFloat<S> {

const FIRST_EIGHT_POWERS: [Limb; 8] = [1, 5, 25, 125, 625, 3125, 15625, 78125];

let mut p5_scratch = vec![];
let mut p5 = vec![FIRST_EIGHT_POWERS[4]];
let mut p5_scratch = smallvec![];
let mut p5: SmallVec<[Limb; 1]> = smallvec![FIRST_EIGHT_POWERS[4]];

let mut r_scratch = vec![];
let mut r = vec![FIRST_EIGHT_POWERS[power & 7]];
let mut r_scratch = smallvec![];
let mut r: SmallVec<[Limb; 1]> = smallvec![FIRST_EIGHT_POWERS[power & 7]];
power >>= 3;

while power > 0 {
Expand Down Expand Up @@ -2064,7 +2065,7 @@ impl<S: Semantics> IeeeFloat<S> {
let calc_precision = (LIMB_BITS << attempt) - 1;
attempt += 1;

let calc_normal_from_limbs = |sig: &mut Vec<Limb>,
let calc_normal_from_limbs = |sig: &mut SmallVec<[Limb; 1]>,
limbs: &[Limb]|
-> StatusAnd<ExpInt> {
sig.resize(limbs_for_bits(calc_precision), 0);
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1 change: 1 addition & 0 deletions src/librustc_apfloat/lib.rs
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Expand Up @@ -53,6 +53,7 @@ extern crate rustc_cratesio_shim;

#[macro_use]
extern crate bitflags;
extern crate smallvec;

use std::cmp::Ordering;
use std::fmt;
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