| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| #![feature(asm)] |
| |
| #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] |
| unsafe fn next_power_of_2(n: u32) -> u32 { |
| let mut tmp = n; |
| asm!("dec $0" : "+rm"(tmp) :: "cc"); |
| let mut shift = 1_u32; |
| while shift <= 16 { |
| asm!( |
| "shr %cl, $2 |
| or $2, $0 |
| shl $$1, $1" |
| : "+&rm"(tmp), "+{ecx}"(shift) : "r"(tmp) : "cc" |
| ); |
| } |
| asm!("inc $0" : "+rm"(tmp) :: "cc"); |
| return tmp; |
| } |
| |
| #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] |
| pub fn main() { |
| unsafe { |
| assert_eq!(64, next_power_of_2(37)); |
| assert_eq!(2147483648, next_power_of_2(2147483647)); |
| } |
| |
| let mut y: isize = 5; |
| let x: isize; |
| unsafe { |
| // Treat the output as initialization. |
| asm!( |
| "shl $2, $1 |
| add $3, $1 |
| mov $1, $0" |
| : "=r"(x), "+r"(y) : "i"(3_usize), "ir"(7_usize) : "cc" |
| ); |
| } |
| assert_eq!(x, 47); |
| assert_eq!(y, 47); |
| |
| let mut x = x + 1; |
| assert_eq!(x, 48); |
| |
| unsafe { |
| // Assignment to mutable. |
| // Early clobber "&": |
| // Forbids the use of a single register by both operands. |
| asm!("shr $$2, $1; add $1, $0" : "+&r"(x) : "r"(x) : "cc"); |
| } |
| assert_eq!(x, 60); |
| } |
| |
| #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))] |
| pub fn main() {} |