From 5fdae0e0b16f281d4c3606b695694f94844067d5 Mon Sep 17 00:00:00 2001
From: "Herman J. Radtke III" <hermanradtke@gmail.com>
Date: Tue, 31 May 2011 11:05:34 -0700
Subject: [PATCH] Add PHP implementation of bfac.

---
 php/bfac.php | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 php/test.php | 42 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 php/bfac.php
 create mode 100644 php/test.php

diff --git a/php/bfac.php b/php/bfac.php
new file mode 100644
index 0000000..b89953d
--- /dev/null
+++ b/php/bfac.php
@@ -0,0 +1,57 @@
+<?php
+
+function valid_factoradic($f)
+{
+    $valid = strrev(implode('', range(0,9)));
+    $max = substr($valid, -strlen($f));
+
+    while (($m = substr($max, -1)) != "") {
+        $max = substr($max, 0, -1);
+        $d = substr($f, -1);
+        $f = substr($f, 0, -1);
+
+        if ($m < $d) {
+            return false;
+        }
+    }
+
+    return ($f <= $max);
+}
+
+function fac2ten($x)
+{
+    $n = 0;
+    $f = 1;
+
+    $d = substr($x, -1);
+    $x = substr($x, 0, -1);
+    while (($d = substr($x, -1)) != "") {
+        $x = substr($x, 0, -1);
+        $n += $d * $f;
+        $f *= $f + 1;
+    }
+
+    return $n;
+}
+
+function ten2fac_r($n, $f)
+{
+    if ($n < $f) {
+        return array("", $n);
+    }
+
+    list($s, $n) = ten2fac_r($n, $f * ($f + 1));
+
+    $d = (int) ($n / $f);
+    $n %= $f;
+    $s .= $d;
+
+    return array($s, $n);
+}
+
+function ten2fac($n)
+{
+    list($f, $n) = ten2fac_r($n, 1);
+
+    return $f . "0";
+}
diff --git a/php/test.php b/php/test.php
new file mode 100644
index 0000000..c7a1167
--- /dev/null
+++ b/php/test.php
@@ -0,0 +1,42 @@
+<?php
+
+require __DIR__ . '/bfac.php';
+
+$expected = array(0, 10, 100, 110, 200, 210, 1000, 1010, 1100, 1110, 1200, 
+    1210, 2000, 2010, 2100, 2110, 2200, 2210, 3000, 3010, 3100, 3110, 3200, 
+    3210);
+
+echo 'ten2fac', PHP_EOL;
+foreach ($expected as $ten => $fac) {
+    $given = ten2fac($ten);
+
+    if ($fac != $given) {
+        echo "Failed: {$ten} => {$fac} returned {$given}", PHP_EOL;
+    }
+}
+
+echo 'fac2ten', PHP_EOL;
+foreach ($expected as $ten => $fac) {
+    $given = fac2ten($fac);
+
+    if ($ten != $given) {
+        echo "Failed: {$ten} => {$fac} returned {$given}", PHP_EOL;
+    }
+}
+
+echo 'valid_factoradic', PHP_EOL;
+foreach ($expected as $ten => $fac) {
+    if( !valid_factoradic($fac)) {
+        echo "Failed: {$fac} returned false", PHP_EOL;
+    }
+
+    $fac += 1;
+    if(valid_factoradic($fac)) {
+        echo "Failed: {$fac} returned true", PHP_EOL;
+    }
+
+    $fac += 19;
+    if(valid_factoradic($fac)) {
+        echo "Failed: {$fac} returned true", PHP_EOL;
+    }
+}