Date: Thu, 5 Dec 2013 09:37:00 -0800 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: freebsd-numerics@freebsd.org Subject: dead code in lgamma_r[f]? Message-ID: <20131205173700.GA64575@troutmask.apl.washington.edu>
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In reviewing the implementation details for lgamma_r[f],
I noticed that in src/e_lgamma.c (and similar code in
e_lgammaf.c):
static double sin_pi(double x)
{
...
} else {
if(ix>=0x43400000) {
y = zero; n = 0; /* y must be even */
} else {
if(ix<0x43300000) z = y+two52; /* exact */
...
}
double
__ieee754_lgamma_r(double x, int *signgamp)
{
...
if(hx<0) {
if(ix>=0x43300000) /* |x|>=2**52, must be -integer */
return one/zero;
t = sin_pi(x);
...
}
sin_pi is only called as shown above. It is appears that
the 'if(ix>=0x43400000)' block is dead code. It also appears
that (if I'm reading the code correctly) the 'if(ix<0x43300000)'
is always true. Thus, if seems that following patch (note
cut-n-paste whitespace munging) should be appropriate:
Index: src/e_lgamma_r.c
===================================================================
--- src/e_lgamma_r.c (revision 1427)
+++ src/e_lgamma_r.c (working copy)
@@ -177,15 +177,11 @@
y = 2.0*(y - floor(y)); /* y = |x| mod 2.0 */
n = (int) (y*4.0);
} else {
- if(ix>=0x43400000) {
- y = zero; n = 0; /* y must be even */
- } else {
- if(ix<0x43300000) z = y+two52; /* exact */
- GET_LOW_WORD(n,z);
- n &= 1;
- y = n;
- n<<= 2;
- }
+ z = y+two52; /* exact */
+ GET_LOW_WORD(n,z);
+ n &= 1;
+ y = n;
+ n<<= 2;
}
switch (n) {
case 0: y = __kernel_sin(pi*y,zero,0); break;
Am I mssing something here?
--
Steve
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