Diff: pki/base64.c

Revision:

0:be515c9019e3

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pki/base64.c	Thu Jul 25 21:16:24 2019 +0000
@@ -0,0 +1,100 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include "base64.h"
+
+char (*Base64ReadNextCharFunctionPointer)(void) = NULL;
+
+static int get6bits()
+{
+    while (true)
+    {
+        char c = Base64ReadNextCharFunctionPointer();
+        if      (c ==  0 ) return -1; //EOF or an error
+        else if (c == '-') return -1; //Finished
+        else if (c == '=') return -1; //Padding  
+        else if (c == '/') return 63;
+        else if (c == '+') return 62;
+        else if (c >= 'a') return c - 'a' + 26;
+        else if (c >= 'A') return c - 'A' +  0;
+        else if (c >= '0') return c - '0' + 52;
+        else continue;
+    }
+}
+
+static int last6 = 0;
+static int posn = 0;
+static bool finished = false;
+int Base64ReadByte()
+{
+    if (finished) return -1;
+    
+    /*
+    L = last
+    T = this
+                out
+    case 0    TTTTTTLL
+    case 1    LLLLTTTT
+    case 2    LLTTTTTT
+    */
+    int this6 = 0;
+    int bits8 = 0;
+    
+    switch (posn)
+    {
+        case 0: //We have no bits leftover
+        {
+            this6 = get6bits(); if (this6 == -1)  return -1; //EOF or an error
+            last6 = get6bits();
+            if (last6 == -1)
+            {
+                last6 = 0;
+                finished = true;
+            }
+            bits8  = this6 << 2;
+            bits8 &= 0xFF;
+            bits8 |= last6 >> 4;
+            
+            posn = 1;
+            break;
+        }
+        case 1: //We have 4 bits leftover
+        {
+            this6 = get6bits(); if (this6 == -1)  return -1; //EOF or an error
+            
+            bits8  = last6 << 4;
+            bits8 &= 0xFF;
+            bits8 |= this6 >> 2;
+            
+            last6 = this6;
+            
+            posn = 2;
+            break;
+        }
+        case 2: //We have 2 bits leftover
+        {
+            this6 = get6bits(); if (this6 == -1)  return -1; //EOF or an error
+            
+            bits8  = last6 << 6;
+            bits8 &= 0xFF;
+            bits8 |= this6;
+            
+            posn = 0;
+            break;
+        }
+    }
+    
+    return bits8;
+}
+int Base64SkipLine()
+{
+    last6 = 0;
+    posn = 0;
+    finished = false;
+    
+    while (true)
+    {
+        char c = Base64ReadNextCharFunctionPointer();
+        if      (c ==   0 ) return -1; //EOF or an error
+        else if (c == '\n') return  0; //EOL
+    }
+}