From 0ce7a9320aab651218585d25738269692017b4ac Mon Sep 17 00:00:00 2001
From: Oscar Najera <hi@oscarnajera.com>
Date: Fri, 6 Jun 2025 17:27:21 +0200
Subject: pointer read length is an argument

With this I don't need to read again the same byte and keep track
of going one byte back
---
 geoip/ip.lisp | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/geoip/ip.lisp b/geoip/ip.lisp
index e00ba89..a61989d 100644
--- a/geoip/ip.lisp
+++ b/geoip/ip.lisp
@@ -42,11 +42,12 @@
   (5am:is (= (parse-ipv4 "8.8.8.8") 134744072))
   (5am:is (= (parse-ipv6 "::1") 1)))
 
-(defparameter *metadata-marker*
-  (concatenate 'vector
-               #(#xab #xcd #xef)
-               (map 'vector #'char-code "MaxMind.com")))
-
+(alexandria:define-constant
+    +metadata-marker+
+    (concatenate 'vector
+                 #(#xab #xcd #xef)
+                 (map 'vector #'char-code "MaxMind.com"))
+  :test #'equalp)
 
 (defstruct maxmind-database
   (filename nil :read-only t)
@@ -153,8 +154,6 @@
          (length (ldb (byte 5 0) control-byte)))
     (when (zerop type)
       (setf type (+ 7 (read-db-char db-ptr))))
-    (when (= type 1)
-      (incf-pointer (db-reader-db-ptr db-ptr) -1))
     (list type
           (cond
             ((or (= type 1) (< length 29))
@@ -177,19 +176,18 @@
 (defun mread-list (db-ptr length)
   (loop repeat length collect (mread-data db-ptr)))
 
-(defun read-pointer (reader)
-  (let* ((control-byte (read-db-char reader))
-         (size-bits (ldb (byte 2 3) control-byte))
-         (value-bits (ldb (byte 3 0) control-byte)))
+(defun read-pointer (reader length)
+  (let ((size-bits (ldb (byte 2 3) length))
+        (value-bits (ldb (byte 3 0) length)))
     (ecase size-bits
       (0 (+ (ash value-bits 8) (read-db-char reader)))
       (1 (+ (ash value-bits 16) (mread-unsigned reader 2) 2048))
       (2 (+ (ash value-bits 24) (mread-unsigned reader 3) 526336))
       (3 (mread-unsigned reader 4)))))
 
-(defun mread-pointer (reader)
+(defun mread-pointer (reader length)
   (with-slots (db-ptr head-ptr data-offset) reader
-    (let* ((target (+ (read-pointer reader) data-offset))
+    (let* ((target (+ (read-pointer reader length) data-offset))
            (curr-ptr db-ptr)
            (result))
       (setf db-ptr (inc-pointer head-ptr target))
@@ -200,7 +198,7 @@
 (defun mread-data (db-ptr)
   (destructuring-bind (type length) (mread-datafield-metadata db-ptr)
     (ecase type
-      (1 (mread-pointer db-ptr))
+      (1 (mread-pointer db-ptr length))
       (2 (mread-uft8 db-ptr length))
       (3 (cons 'double (mread-unsigned db-ptr 8)))
       (4 (bytes-from-foreign db-ptr length))
-- 
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