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//! Architecture-specific support for x86-32 without SSE2
//!
//! We use an alternative implementation on x86, because the
//! main implementation fails with the x87 FPU used by
//! debian i386, probably due to excess precision issues.
//!
//! See https://github.com/rust-lang/compiler-builtins/pull/976 for discussion on why these
//! functions are implemented in this way.
pub fn ceil(mut x: f64) -> f64 {
unsafe {
core::arch::asm!(
"fld qword ptr [{x}]",
// Save the FPU control word, using `x` as scratch space.
"fstcw [{x}]",
// Set rounding control to 0b10 (+∞).
"mov word ptr [{x} + 2], 0x0b7f",
"fldcw [{x} + 2]",
// Round.
"frndint",
// Restore FPU control word.
"fldcw [{x}]",
// Save rounded value to memory.
"fstp qword ptr [{x}]",
x = in(reg) &mut x,
// All the x87 FPU stack is used, all registers must be clobbered
out("st(0)") _, out("st(1)") _,
out("st(2)") _, out("st(3)") _,
out("st(4)") _, out("st(5)") _,
out("st(6)") _, out("st(7)") _,
options(nostack),
);
}
x
}
pub fn floor(mut x: f64) -> f64 {
unsafe {
core::arch::asm!(
"fld qword ptr [{x}]",
// Save the FPU control word, using `x` as scratch space.
"fstcw [{x}]",
// Set rounding control to 0b01 (-∞).
"mov word ptr [{x} + 2], 0x077f",
"fldcw [{x} + 2]",
// Round.
"frndint",
// Restore FPU control word.
"fldcw [{x}]",
// Save rounded value to memory.
"fstp qword ptr [{x}]",
x = in(reg) &mut x,
// All the x87 FPU stack is used, all registers must be clobbered
out("st(0)") _, out("st(1)") _,
out("st(2)") _, out("st(3)") _,
out("st(4)") _, out("st(5)") _,
out("st(6)") _, out("st(7)") _,
options(nostack),
);
}
x
}
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