From 8f86cc6e51a549697213795b749ba30bd4deab1a Mon Sep 17 00:00:00 2001
From: Erik Charlebois <erikcharlebois@gmail.com>
Date: Sat, 13 Feb 2010 19:47:44 -0800
Subject: [PATCH] Made p^ more efficient by repeated squaring instead of
 repeated multiplication

---
 basis/math/polynomials/polynomials-tests.factor |  1 +
 basis/math/polynomials/polynomials.factor       | 13 +++++++------
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/basis/math/polynomials/polynomials-tests.factor b/basis/math/polynomials/polynomials-tests.factor
index e0cedb9adf..08f81a5bfa 100644
--- a/basis/math/polynomials/polynomials-tests.factor
+++ b/basis/math/polynomials/polynomials-tests.factor
@@ -17,6 +17,7 @@ IN: math.polynomials.tests
 [ { 4 8 0 12 } ] [ 4 { 1 2 0 3 } n*p ] unit-test
 [ { 1 4 4 0 0 } ] [ { 1 2 0 } p-sq ] unit-test
 [ { 1 6 12 8 0 0 0 } ] [ { 1 2 0 } 3 p^ ] unit-test
+[ { 1 } ] [ { 1 2 0 } 0 p^ ] unit-test
 [ { 1 4 7 6 0 0 0 0 0 } ] [ { 1 2 3 0 0 0 } { 1 2 0 0 } p* ] unit-test
 [ V{ 7 -2 1 } V{ -20 0 0 } ] [ { 1 1 1 1 } { 3 1 } p/mod ] unit-test
 [ V{ 0 0 } V{ 1 1 } ] [ { 1 1 } { 1 1 1 1 } p/mod ] unit-test
diff --git a/basis/math/polynomials/polynomials.factor b/basis/math/polynomials/polynomials.factor
index 694b9ef542..b994410283 100644
--- a/basis/math/polynomials/polynomials.factor
+++ b/basis/math/polynomials/polynomials.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2008 Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: arrays kernel make math math.order math.vectors sequences
-    splitting vectors macros combinators ;
+splitting vectors macros combinators math.bits ;
 IN: math.polynomials
 
 <PRIVATE
@@ -40,12 +40,13 @@ PRIVATE>
 
 ERROR: negative-power-polynomial p n ;
 
+: (p^) ( p n  -- p^n )
+    make-bits { 1 } [ [ over p* ] when [ p-sq ] dip ] reduce nip ;
+
 : p^ ( p n -- p^n )
-    {
-        { [ dup 0 > ] [ 1 - dupd [ p* ] with times ] }
-        { [ dup 0 = ] [ 2drop { 1 } ] }
-        { [ dup 0 < ] [ negative-power-polynomial ] }
-    } cond ;
+    dup 0 >=
+    [ (p^) ]
+    [ negative-power-polynomial ] if ;
 
 <PRIVATE