[libmath-prime-util-perl] 16/59: Do a mod before power operations -- avoids fp exception for very large bases on small n

[Partha P. Mukherjee]

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ppm-guest pushed a commit to annotated tag v0.10
in repository libmath-prime-util-perl.

commit 8e2236731c187ca78272f635217fe95f3eb2af10
Author: Dana Jacobsen <dana at acm.org>
Date:   Sat Jun 30 15:23:31 2012 -0600

    Do a mod before power operations -- avoids fp exception for very large bases on small n
---
 factor.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/factor.c b/factor.c
index 4f49763..ce55363 100644
--- a/factor.c
+++ b/factor.c
@@ -141,6 +141,7 @@ int trial_factor(UV n, UV *factors, UV maxtrial)
 #ifndef HALF_WORD
   static UV powmod(UV n, UV power, UV m) {
     UV t = 1;
+    n %= m;
     while (power) {
       if (power & 1)
         t = mulmod(t, n, m);
@@ -152,8 +153,8 @@ int trial_factor(UV n, UV *factors, UV maxtrial)
 #else
   static UV powmod(UV n, UV power, UV m) {
     UV t = 1;
+    n %= m;
     if (m < HALF_WORD) {
-      n %= m;
       while (power) {
         if (power & 1)
           t = (t*n)%m;

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