guile: Add (net ricketyspace taocp utils mix) module.

* guile/net/ricketyspace/taocp/utils/mix.scm: New file.

1 files changed, 25 insertions, 0 deletions

diff --git a/guile/net/ricketyspace/taocp/utils/mix.scm b/guile/net/ricketyspace/taocp/utils/mix.scm
new file mode 100644
index 0000000..c92a61b
--- /dev/null
+++ b/guile/net/ricketyspace/taocp/utils/mix.scm
@@ -0,0 +1,25 @@
+;;;; copyright 2016 rsiddharth <s@ricketyspace.net>
+;;;; under gnu general public license version 3 or higher.
+
+(define-module (net ricketyspace taocp utils mix)
+  #:use-module (srfi srfi-13)
+  #:use-module (srfi srfi-1)
+  #:export (word-to-decimal
+            nth-byte))
+
+;;;; Functions that facilitate hacking in MIX
+
+;;; All functions in this module assume that a byte is 6 bits.
+
+(define (word-to-decimal word)
+  "Converts WORD to a decimal number.
+
+WORD must be a string in this format:
+
+    ±:00:00:00:00:00"
+  (let ((bytes (string-split word #\:)))
+    (fold (lambda (byte-number d)
+            (+ (* (expt (expt 2 6) (- 4 byte-number))
+                  (string->number (list-ref bytes byte-number)))
+               d))
+          0 (iota 5))))