1 files changed, 54 insertions, 0 deletions
diff --git a/utils/base64_decode_atom.c b/utils/base64_decode_atom.c
new file mode 100644
index 00000000..2a98150e
--- /dev/null
+++ b/utils/base64_decode_atom.c
@@ -0,0 +1,54 @@
+/*
+ * Core routine to decode a single atomic base64 chunk.
+ */
+
+#include "defs.h"
+#include "misc.h"
+
+int base64_decode_atom(const char *atom, unsigned char *out)
+{
+    int vals[4];
+    int i, v, len;
+    unsigned word;
+    char c;
+
+    for (i = 0; i < 4; i++) {
+        c = atom[i];
+        if (c >= 'A' && c <= 'Z')
+            v = c - 'A';
+        else if (c >= 'a' && c <= 'z')
+            v = c - 'a' + 26;
+        else if (c >= '0' && c <= '9')
+            v = c - '0' + 52;
+        else if (c == '+')
+            v = 62;
+        else if (c == '/')
+            v = 63;
+        else if (c == '=')
+            v = -1;
+        else
+            return 0;                  /* invalid atom */
+        vals[i] = v;
+    }
+
+    if (vals[0] == -1 || vals[1] == -1)
+        return 0;
+    if (vals[2] == -1 && vals[3] != -1)
+        return 0;
+
+    if (vals[3] != -1)
+        len = 3;
+    else if (vals[2] != -1)
+        len = 2;
+    else
+        len = 1;
+
+    word = ((vals[0] << 18) |
+            (vals[1] << 12) | ((vals[2] & 0x3F) << 6) | (vals[3] & 0x3F));
+    out[0] = (word >> 16) & 0xFF;
+    if (len > 1)
+        out[1] = (word >> 8) & 0xFF;
+    if (len > 2)
+        out[2] = word & 0xFF;
+    return len;
+}