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Reduces Code Repetitions like !n >> amt #59101

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merged 4 commits into from
Mar 13, 2019
Merged

Reduces Code Repetitions like !n >> amt #59101

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749e9d4
added a function for reducing repetition of bit operation
kenta7777 Mar 11, 2019
4c9f7a0
reduced some code repetitions of bit operation
kenta7777 Mar 11, 2019
0ede9e6
replaced some bit operations with truncate
kenta7777 Mar 11, 2019
18b40c6
removed the definition of mask
kenta7777 Mar 11, 2019
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6 changes: 6 additions & 0 deletions src/librustc/mir/interpret/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -434,3 +434,9 @@ pub fn truncate(value: u128, size: Size) -> u128 {
// truncate (shift left to drop out leftover values, shift right to fill with zeroes)
(value << shift) >> shift
}

pub fn mask(size: Size) -> u128 {
let size = size.bits();
let shift = 128 - size;
!0u128 >> shift
}
5 changes: 3 additions & 2 deletions src/librustc_mir/build/matches/simplify.rs
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Expand Up @@ -19,6 +19,7 @@ use rustc::ty;
use rustc::ty::layout::{Integer, IntegerExt, Size};
use syntax::attr::{SignedInt, UnsignedInt};
use rustc::hir::RangeEnd;
use rustc::mir::interpret::mask;

use std::mem;

Expand Down Expand Up @@ -115,14 +116,14 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
ty::Int(ity) => {
// FIXME(49937): refactor these bit manipulations into interpret.
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These FIXMEs look resolved now.

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Thank you for reporting. I forgot to remove this comment out.

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I think let bias = 1u128 << (size.bits() - 1); is not resolved.

let size = Integer::from_attr(&tcx, SignedInt(ity)).size();
let max = !0u128 >> (128 - size.bits());
let max = mask(size);
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this could be truncate(u128::max_value(), size)

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Thank you for your review. Then, should I replace mask with truncate and remove the definition of mask?

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yes, I think that's for the best, unless you see a lot of other sites in the compiler where using mask would make sense.

let bias = 1u128 << (size.bits() - 1);
(Some((0, max, size)), bias)
}
ty::Uint(uty) => {
// FIXME(49937): refactor these bit manipulations into interpret.
let size = Integer::from_attr(&tcx, UnsignedInt(uty)).size();
let max = !0u128 >> (128 - size.bits());
let max = mask(size);
(Some((0, max, size)), 0)
}
_ => (None, 0),
Expand Down