acos.s fix: use the formula acos(x) = atan2(sqrt(1-x),sqrt(1+x))

the old formula atan2(1,sqrt((1+x)/(1-x))) was faster but could give nan result at x=1 when the rounding mode is FE_DOWNWARD (so 1-1 == -0 and 2/-0 == -inf), the new formula gives -0 at x=+-1 with downward rounding.
14 years ago · a4a0c91275
2 changed files with 2 additions and 6 deletions
--- a/src/math/i386/acos.s
+++ b/src/math/i386/acos.s
@ -18,12 +18,10 @@ acos:
 	fld %st(1)
 	fld1
 	fsubp
+	fsqrt
 	fxch %st(2)
 	faddp
-	fdivp
 	fsqrt
-	fld1
-	fxch %st(1)
 	fpatan
 	fld1
 	fld1
--- a/src/math/x86_64/acosl.s
+++ b/src/math/x86_64/acosl.s
@ -6,12 +6,10 @@ acosl:
 	fld %st(1)
 	fld1
 	fsubp
+	fsqrt
 	fxch %st(2)
 	faddp
-	fdivp
 	fsqrt
-	fld1
-	fxch %st(1)
 	fpatan
 	fld1
 	fld1