Fix expm1 spurious underflow exceptions (bug 6778).

[thirdparty/glibc.git] / sysdeps / i386 / fpu / s_expm1.S

diff --git a/sysdeps/i386/fpu/s_expm1.S b/sysdeps/i386/fpu/s_expm1.S
index 9883f9b353c44d8b007a2199b8a60f6b4ea606e7..d2754de911134b9305a15da3bc1498b22dc800af 100644 (file)
--- a/sysdeps/i386/fpu/s_expm1.S
+++ b/sysdeps/i386/fpu/s_expm1.S
@@ -51,19 +51,31 @@ ENTRY(__expm1)
        jae     HIDDEN_JUMPTARGET (__exp)
 
        fldl    4(%esp)         // x
-       fxam                    // Is NaN or +-Inf?
+       fxam                    // Is NaN, +-Inf or +-0?
+       xorb    $0x80, %ah
+       cmpl    $0xc043, %eax   // is num <= -38.0?
        fstsw   %ax
        movb    $0x45, %ch
+       jb      4f
+
+       // Below -38.0 (may be -NaN or -Inf).
+       andb    %ah, %ch
+#ifdef PIC
+       LOAD_PIC_REG (dx)
+#endif
+       cmpb    $0x01, %ch
+       je      5f              // If -NaN, jump.
+       jmp     2f              // -large, possibly -Inf.
+
+4:     // In range -38.0 to 704.0 (may be +-0 but not NaN or +-Inf).
        andb    %ah, %ch
        cmpb    $0x40, %ch
        je      3f              // If +-0, jump.
 #ifdef PIC
        LOAD_PIC_REG (dx)
 #endif
-       cmpb    $0x05, %ch
-       je      2f              // If +-Inf, jump.
 
-       fldt    MO(l2e)         // log2(e) : x
+5:     fldt    MO(l2e)         // log2(e) : x
        fmulp                   // log2(e)*x
        fld     %st             // log2(e)*x : log2(e)*x
        frndint                 // int(log2(e)*x) : log2(e)*x
@@ -79,9 +91,7 @@ ENTRY(__expm1)
        fsubrp  %st, %st(1)     // 2^(log2(e)*x)
        ret
 
-2:     testl   $0x200, %eax    // Test sign.
-       jz      3f              // If positive, jump.
-       fstp    %st
+2:     fstp    %st
        fldl    MO(minus1)      // Set result to -1.0.
 3:     ret
 END(__expm1)