From d593e5dfa9d3d2538beb18c4ea90d7a809b20aff Mon Sep 17 00:00:00 2001
From: Bartosz Taudul <wolf.pld@gmail.com>
Date: Fri, 28 Jun 2019 21:57:38 +0200
Subject: [PATCH] DXT1 SIMD color index table generator.

---
 extra/dxt1table.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 extra/dxt1table.c

diff --git a/extra/dxt1table.c b/extra/dxt1table.c
new file mode 100644
index 00000000..6cf2a647
--- /dev/null
+++ b/extra/dxt1table.c
@@ -0,0 +1,36 @@
+#include <stdint.h>
+#include <stdio.h>
+
+static const uint8_t IndexTable[4] = { 1, 3, 2, 0 };
+
+int convert( int v )
+{
+    int v0 = v & 0x3;
+    int v1 = ( v >> 2 ) & 0x3;
+    int v2 = ( v >> 4 ) & 0x3;
+    int v3 = ( v >> 6 );
+
+    int t0 = IndexTable[v0];
+    int t1 = IndexTable[v1];
+    int t2 = IndexTable[v2];
+    int t3 = IndexTable[v3];
+
+    return t0 | ( t1 << 2 ) | ( t2 << 4 ) | ( t3 << 6 );
+}
+
+int main()
+{
+    for( int i=0; i<256; i++ )
+    {
+        if( i % 16 == 15 )
+        {
+            printf( "%i,\n", convert( i ) );
+        }
+        else
+        {
+            printf( "%i,\t", convert( i ) );
+        }
+    }
+    printf( "\n" );
+    return 0;
+}