Skip to content

implement floor and ceil in assembly on i586 #976

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: master
Choose a base branch
from
Open

implement floor and ceil in assembly on i586 #976

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 0 additions & 22 deletions libm-test/src/precision.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -271,18 +271,6 @@ impl MaybeOverride<(f32,)> for SpecialCase {

impl MaybeOverride<(f64,)> for SpecialCase {
fn check_float<F: Float>(input: (f64,), actual: F, expected: F, ctx: &CheckCtx) -> CheckAction {
if cfg!(x86_no_sse)
&& ctx.base_name == BaseName::Ceil
&& ctx.basis == CheckBasis::Musl
&& input.0 < 0.0
&& input.0 > -1.0
&& expected == F::ZERO
&& actual == F::ZERO
{
// musl returns -0.0, we return +0.0
return XFAIL("i586 ceil signed zero");
}

if cfg!(x86_no_sse)
&& (ctx.base_name == BaseName::Rint || ctx.base_name == BaseName::Roundeven)
&& (expected - actual).abs() <= F::ONE
Expand All @@ -292,16 +280,6 @@ impl MaybeOverride<(f64,)> for SpecialCase {
return XFAIL("i586 rint rounding mode");
}

if cfg!(x86_no_sse)
&& (ctx.fn_ident == Identifier::Ceil || ctx.fn_ident == Identifier::Floor)
&& expected.eq_repr(F::NEG_ZERO)
&& actual.eq_repr(F::ZERO)
{
// FIXME: the x87 implementations do not keep the distinction between -0.0 and 0.0.
// See https://github.com/rust-lang/libm/pull/404#issuecomment-2572399955
return XFAIL("i586 ceil/floor signed zero");
}

if cfg!(x86_no_sse)
&& (ctx.fn_ident == Identifier::Exp10 || ctx.fn_ident == Identifier::Exp2)
{
Expand Down
78 changes: 52 additions & 26 deletions libm/src/math/arch/i586.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,37 +1,63 @@
//! Architecture-specific support for x86-32 without SSE2

use super::super::fabs;

/// 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.
/// Basic implementation taken from https://github.com/rust-lang/libm/issues/219.
pub fn ceil(x: f64) -> f64 {
if fabs(x).to_bits() < 4503599627370496.0_f64.to_bits() {
let truncated = x as i64 as f64;
if truncated < x {
return truncated + 1.0;
} else {
return truncated;
}
} else {
return x;
}
/// Based on https://github.com/NetBSD/src/blob/trunk/lib/libm/arch/i387/s_ceil.S
#[unsafe(naked)]
pub extern "C" fn ceil(_: f64) -> f64 {
core::arch::naked_asm!(
"pushl %ebp",
"movl %esp,%ebp",
"subl $8,%esp",
// Store fpu control word.
"fstcw -4(%ebp)",
"movw -4(%ebp),%dx",
// Round towards +oo.
"orw $0x0800,%dx",
"andw $0xfbff,%dx",
"movw %dx,-8(%ebp)",
// Load modified control word
"fldcw -8(%ebp)",
// Round.
"fldl 8(%ebp)",
"frndint",
// Restore original control word.
"fldcw -4(%ebp)",
//
"leave",
"ret",
options(att_syntax)
)
}

/// 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.
/// Basic implementation taken from https://github.com/rust-lang/libm/issues/219.
pub fn floor(x: f64) -> f64 {
if fabs(x).to_bits() < 4503599627370496.0_f64.to_bits() {
let truncated = x as i64 as f64;
if truncated > x {
return truncated - 1.0;
} else {
return truncated;
}
} else {
return x;
}
/// Based on https://github.com/NetBSD/src/blob/trunk/lib/libm/arch/i387/s_floor.S
#[unsafe(naked)]
pub extern "C" fn floor(_: f64) -> f64 {
core::arch::naked_asm!(
"pushl %ebp",
"movl %esp,%ebp",
"subl $8,%esp",
// Store fpu control word.
"fstcw -4(%ebp)",
"movw -4(%ebp),%dx",
// Round towards -oo.
"orw $0x0400,%dx",
"andw $0xf7ff,%dx",
"movw %dx,-8(%ebp)",
// Load modified control word
"fldcw -8(%ebp)",
// Round.
"fldl 8(%ebp)",
"frndint",
// Restore original control word.
"fldcw -4(%ebp)",
//
"leave",
"ret",
options(att_syntax)
)
}
Loading