57 lines
1.3 KiB
Rust
57 lines
1.3 KiB
Rust
// run-pass
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#![feature(asm)]
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#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
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unsafe fn next_power_of_2(n: u32) -> u32 {
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let mut tmp = n;
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asm!("dec $0" : "+rm"(tmp) :: "cc");
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let mut shift = 1_u32;
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while shift <= 16 {
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asm!(
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"shr %cl, $2
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or $2, $0
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shl $$1, $1"
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: "+&rm"(tmp), "+{ecx}"(shift) : "r"(tmp) : "cc"
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);
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}
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asm!("inc $0" : "+rm"(tmp) :: "cc");
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return tmp;
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}
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#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
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pub fn main() {
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unsafe {
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assert_eq!(64, next_power_of_2(37));
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assert_eq!(2147483648, next_power_of_2(2147483647));
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}
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let mut y: isize = 5;
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let x: isize;
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unsafe {
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// Treat the output as initialization.
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asm!(
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"shl $2, $1
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add $3, $1
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mov $1, $0"
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: "=r"(x), "+r"(y) : "i"(3_usize), "ir"(7_usize) : "cc"
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);
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}
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assert_eq!(x, 47);
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assert_eq!(y, 47);
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let mut x = x + 1;
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assert_eq!(x, 48);
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unsafe {
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// Assignment to mutable.
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// Early clobber "&":
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// Forbids the use of a single register by both operands.
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asm!("shr $$2, $1; add $1, $0" : "+&r"(x) : "r"(x) : "cc");
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}
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assert_eq!(x, 60);
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}
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#[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
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pub fn main() {}
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