Update libm/src/math/arch/i586.rs

tgross35 · quaternic · tgross35 · commit 45bec817b4e7 · 2025-12-06T01:55:21.000-05:00
Co-authored-by: Juho Kahala &lt;57393910+quaternic@users.noreply.github.com&gt;
diff --git a/libm/src/math/arch/i586.rs b/libm/src/math/arch/i586.rs
@@ -60,7 +60,12 @@ pub fn floor(mut x: f64) -> f64 {
     }
     x
 }
-
+/// Implements the exponential functions with `x87` assembly. This relies on
+/// the instruction `f2xm1`, which computes `2^x - 1` (for |x| < 1). This
+/// transcendental instruction is documented to produce results with error
+/// below 1ulp (in the native double-extended precision format).
+/// This translates to correctly rounded results for f32, but results
+/// in f64 may have 1ulp error, which may depend on the hardware.
 macro_rules! x87exp {
     ($float_ty:ident, $word_size:literal, $fn_name:ident,  $load_op:literal) => {
         pub fn $fn_name(mut x: $float_ty) -> $float_ty { unsafe {

Original file line number	Diff line number	Diff line change
`@@ -60,7 +60,12 @@ pub fn floor(mut x: f64) -> f64 {`
`60`	`60`	`}`
`61`	`61`	`x`
`62`	`62`	`}`
`63`		`-`
	`63`	+/// Implements the exponential functions with `x87` assembly. This relies on
	`64`	+/// the instruction `f2xm1`, which computes `2^x - 1` (for \|x\| < 1). This
	`65`	`+/// transcendental instruction is documented to produce results with error`
	`66`	`+/// below 1ulp (in the native double-extended precision format).`
	`67`	`+/// This translates to correctly rounded results for f32, but results`
	`68`	`+/// in f64 may have 1ulp error, which may depend on the hardware.`
`64`	`69`	`macro_rules! x87exp {`
`65`	`70`	`($float_ty:ident, $word_size:literal, $fn_name:ident, $load_op:literal) => {`
`66`	`71`	`pub fn $fn_name(mut x: $float_ty) -> $float_ty { unsafe {`