More efficient polyval algorithm in math.polynomials

2011-02-12 22:41:13 -06:00 · 2011-02-12 22:41:13 -06:00 · fd7e5ffee8
parent 02ecc45165
commit fd7e5ffee8
2 changed files with 10 additions and 1 deletions
--- a/basis/math/polynomials/polynomials-tests.factor
+++ b/basis/math/polynomials/polynomials-tests.factor
@ -33,3 +33,9 @@ IN: math.polynomials.tests

 [ { 10 200 3000 } ] [ { 1 10 100 1000 } pdiff ] unit-test

+
+[ { -512 2304 -4608 5376 -4032 2016 -672 144 -18 1 } ]
+[ { -2 1 } 9 p^ ] unit-test
+
+[ 0 ]
+[ 2 { -2 1 } 9 p^ polyval ] unit-test
--- a/basis/math/polynomials/polynomials.factor
+++ b/basis/math/polynomials/polynomials.factor
@ -91,7 +91,10 @@ PRIVATE>
    dup length iota v* rest ;

 : polyval ( x p -- p[x] )
-    [ length swap powers ] [ nip ] 2bi v. ;
+    ! Horner scheme
+    [ nip <reversed> unclip-slice swap ]
+    [ drop ] 2bi
+    '[ [ _ * ] dip + ] each ;

 MACRO: polyval* ( p -- )
    reverse