Add base64 encoders and decoders

1 files changed, 118 insertions, 0 deletions

diff --git a/src/base64.cpp b/src/base64.cpp
new file mode 100644
index 0000000..6428424
--- /dev/null
+++ b/src/base64.cpp
@@ -0,0 +1,118 @@
+#include "axolotl/base64.hh"
+
+
+namespace {
+
+static const std::uint8_t ENCODE_BASE64[64] = {
+    0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
+    0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F, 0x50,
+    0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
+    0x59, 0x5A, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
+    0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E,
+    0x6F, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76,
+    0x77, 0x78, 0x79, 0x7A, 0x30, 0x31, 0x32, 0x33,
+    0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2B, 0x2F,
+};
+
+static const std::uint8_t E = -1;
+
+static const std::uint8_t DECODE_BASE64[128] = {
+/*  0x0 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xA 0xB 0xC 0xD 0xE 0xF */
+     E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,
+     E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E,
+     E,  E,  E,  E,  E,  E,  E,  E,  E,  E,  E, 62,  E,  E,  E, 63,
+    52, 53, 54, 55, 56, 57, 58, 59, 60, 61,  E,  E,  E,  E,  E,  E,
+     E,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
+    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,  E,  E,  E,  E,  E,
+     E, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
+    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,  E,  E,  E,  E,  E,
+};
+
+} // namespace
+
+
+std::size_t axolotl::encode_base64_length(
+    std::size_t input_length
+) {
+    return 4 * ((input_length + 2) / 3) + (input_length + 2) % 3 - 2;
+}
+
+
+void axolotl::encode_base64(
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::uint8_t const * end = input + (input_length / 3) * 3;
+    std::uint8_t const * pos = input;
+    while (pos != end) {
+        unsigned value = pos[0];
+        value <<= 8; value |= pos[1];
+        value <<= 8; value |= pos[2];
+        pos += 3;
+        output[3] = ENCODE_BASE64[value & 0x3F];
+        value >>= 6; output[2] = ENCODE_BASE64[value & 0x3F];
+        value >>= 6; output[1] = ENCODE_BASE64[value & 0x3F];
+        value >>= 6; output[0] = ENCODE_BASE64[value];
+        output += 4;
+    }
+    unsigned remainder = input + input_length - pos;
+    if (remainder) {
+        unsigned value = pos[0];
+        if (remainder == 2) {
+            value <<= 8; value |= pos[1];
+            value <<= 2;
+            output[2] = ENCODE_BASE64[value & 0x3F];
+            value >>= 6;
+        } else {
+            value <<= 4;
+        }
+        output[1] = ENCODE_BASE64[value & 0x3F];
+        value >>= 6;
+        output[0] = ENCODE_BASE64[value];
+    }
+}
+
+
+std::size_t axolotl::decode_base64_length(
+    std::size_t input_length
+) {
+    if (input_length % 4 == 1) {
+        return std::size_t(-1);
+    } else {
+        return 3 * ((input_length + 2) / 4) + (input_length + 2) % 4 - 2;
+    }
+}
+
+
+void axolotl::decode_base64(
+    std::uint8_t const * input, std::size_t input_length,
+    std::uint8_t * output
+) {
+    std::uint8_t const * end = input + (input_length / 4) * 4;
+    std::uint8_t const * pos = input;
+    while (pos != end) {
+        unsigned value = DECODE_BASE64[pos[0] & 0x7F];
+        value <<= 6; value |= DECODE_BASE64[pos[1] & 0x7F];
+        value <<= 6; value |= DECODE_BASE64[pos[2] & 0x7F];
+        value <<= 6; value |= DECODE_BASE64[pos[3] & 0x7F];
+        pos += 4;
+        output[2] = value;
+        value >>= 8; output[1] = value;
+        value >>= 8; output[0] = value;
+        output += 3;
+    }
+    unsigned remainder = input + input_length - pos;
+    if (remainder) {
+        unsigned value = DECODE_BASE64[pos[0] & 0x7F];
+        value <<= 6; value |= DECODE_BASE64[pos[1] & 0x7F];
+        if (remainder == 3) {
+            value <<= 6; value |= DECODE_BASE64[pos[2] & 0x7F];
+            value >>= 2;
+            output[1] = value;
+            value >>= 8;
+        } else {
+            value >>= 4;
+        }
+        output[0] = value;
+    }
+}