From 1dc79e2b410c4512e2d9cafae1fe5aa619cacef5 Mon Sep 17 00:00:00 2001
From: Rudolf Polzer <divVerent@xonotic.org>
Date: Sun, 12 Jun 2011 14:02:33 +0200
Subject: [PATCH] add "xencoding", an encoding scheme of numbers into invisible
 parts of messages

---
 qcsrc/common/util.qc | 34 ++++++++++++++++++++++++++++++++++
 qcsrc/common/util.qh |  7 +++++++
 2 files changed, 41 insertions(+)

diff --git a/qcsrc/common/util.qc b/qcsrc/common/util.qc
index 89cb92baf..23d4f3431 100644
--- a/qcsrc/common/util.qc
+++ b/qcsrc/common/util.qc
@@ -2017,3 +2017,37 @@ string CTX(string s)
 		return s;
 	return substring(s, p+1, -1);
 }
+
+// x-encoding (encoding as zero length invisible string)
+const string XENCODE_2  = "xX";
+const string XENCODE_22 = "0123456789abcdefABCDEF";
+string xencode(float f)
+{
+	float a, b, c, d;
+	d = mod(f, 22); f = floor(f / 22);
+	c = mod(f, 22); f = floor(f / 22);
+	b = mod(f, 22); f = floor(f / 22);
+	a = mod(f,  2); // f = floor(f /  2);
+	return strcat(
+		"^",
+		substring(XENCODE_2,  a, 1),
+		substring(XENCODE_22, b, 1),
+		substring(XENCODE_22, c, 1),
+		substring(XENCODE_22, d, 1)
+	);
+}
+float xdecode(string s)
+{
+	float a, b, c, d;
+	if(substring(s, 0, 1) != "^")
+		return -1;
+	if(strlen(s) < 5)
+		return -1;
+	a = strstrofs(XENCODE_2,  substring(s, 1, 1), 0);
+	b = strstrofs(XENCODE_22, substring(s, 2, 1), 0);
+	c = strstrofs(XENCODE_22, substring(s, 3, 1), 0);
+	d = strstrofs(XENCODE_22, substring(s, 4, 1), 0);
+	if(a < 0 || b < 0 || c < 0 || d < 0)
+		return -1;
+	return ((a * 22 + b) * 22 + c) * 22 + d;
+}
diff --git a/qcsrc/common/util.qh b/qcsrc/common/util.qh
index 49afad22d..5a5792cb7 100644
--- a/qcsrc/common/util.qh
+++ b/qcsrc/common/util.qh
@@ -258,3 +258,10 @@ string prvm_language;
 string language_filename(string s);
 string CTX(string s);
 #define ZCTX(s) strzone(CTX(s))
+
+// x-encoding (encoding as zero length invisible string)
+// encodes approx. 14 bits into 5 bytes of color code string
+const float XENCODE_MAX = 21295; // 2*22*22*22-1
+const float XENCODE_LEN = 5;
+string xencode(float f);
+float xdecode(string s);
-- 
2.39.2