bjoernager/rust
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u128 truncation and sign extension are not just interpreter related

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This commit is contained in:
oli 2020-11-04 13:41:58 +00:00
parent e67c768110
commit abacaf2aef
18 changed files with 73 additions and 89 deletions
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35
compiler/rustc_middle/src/mir/interpret/mod.rs
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@ -110,7 +110,7 @@ use rustc_hir::def_id::DefId;
use rustc_macros::HashStable;
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_serialize::{Decodable, Encodable};
use rustc_target::abi::{Endian, Size};
use rustc_target::abi::Endian;
use crate::mir;
use crate::ty::codec::{TyDecoder, TyEncoder};
@ -590,39 +590,6 @@ pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, i
uint
}
////////////////////////////////////////////////////////////////////////////////
// Methods to facilitate working with signed integers stored in a u128
////////////////////////////////////////////////////////////////////////////////
/// Truncates `value` to `size` bits and then sign-extend it to 128 bits
/// (i.e., if it is negative, fill with 1's on the left).
#[inline]
pub fn sign_extend(value: u128, size: Size) -> u128 {
let size = size.bits();
if size == 0 {
// Truncated until nothing is left.
return 0;
}
// Sign-extend it.
let shift = 128 - size;
// Shift the unsigned value to the left, then shift back to the right as signed
// (essentially fills with FF on the left).
(((value << shift) as i128) >> shift) as u128
}
/// Truncates `value` to `size` bits.
#[inline]
pub fn truncate(value: u128, size: Size) -> u128 {
let size = size.bits();
if size == 0 {
// Truncated until nothing is left.
return 0;
}
let shift = 128 - size;
// Truncate (shift left to drop out leftover values, shift right to fill with zeroes).
(value << shift) >> shift
}
/// Computes the unsigned absolute value without wrapping or panicking.
#[inline]
pub fn uabs(value: i64) -> u64 {