From a7909b294966eb861ce174aaa2c4696cb7cfa865 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Tom=C3=A1s?= <jtomas1815@gmail.com>
Date: Fri, 7 Nov 2025 06:11:09 -0300
Subject: Bit stream decoder

---
 common.lisp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

(limited to 'common.lisp')

diff --git a/common.lisp b/common.lisp
index a061ca1..1c11703 100644
--- a/common.lisp
+++ b/common.lisp
@@ -7,3 +7,15 @@
 (defstruct point
   (offset 0 :type fixnum)
   (size 0 :type fixnum))
+
+(declaim (ftype (function ((array (unsigned-byte 1)) fixnum) (unsigned-byte 8)) bits->byte))
+(defun bits->byte (data index)
+  (let ((byte 0))
+    (dotimes (i 8)
+      (setf byte (logior byte (ash (elt data (+ index i)) (- 7 i)))))
+    byte))
+
+(declaim (ftype (function ((unsigned-byte 8) (array (unsigned-byte 1)) fixnum)) byte->bits))
+(defun byte->bits (data bits index)
+  (dotimes (i 8)
+    (setf (elt bits (+ index i)) (ash (logand data (ash 1 (- 7 i))) (- i 7)))))
-- 
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