From cfb10566fdb3093363fc39d21a8c5aa5c4deeeeb Mon Sep 17 00:00:00 2001
From: Rutger Broekhoff
Date: Fri, 21 May 2021 00:16:17 +0200
Subject: Initial commit

---
 src/base32.zig | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 src/base32.zig

(limited to 'src/base32.zig')

diff --git a/src/base32.zig b/src/base32.zig
new file mode 100644
index 0000000..b1400a5
--- /dev/null
+++ b/src/base32.zig
@@ -0,0 +1,120 @@
+const std = @import("std");
+
+// TODO(rutgerbrf): simplify the code of the encoder & decoder?
+
+pub const Encoder = struct {
+    const Self = @This();
+
+    out_off: u4 = 0,
+    buf: u5 = 0,
+
+    pub fn write(self: *Self, b: u8, out: []u8) usize {
+        var i: usize = 0;
+        var bits_left: u4 = 8;
+        while (bits_left > 0) {
+            var space_avail = @truncate(u3, 5 - self.out_off);
+            var write_bits: u3 = if (bits_left < space_avail) @truncate(u3, bits_left) else space_avail;
+            bits_left -= write_bits;
+            var mask: u8 = (@as(u8, 0x01) << write_bits) - 1;
+            var want: u8 = (b >> @truncate(u3, bits_left)) & mask;
+            self.buf |= @truncate(u5, want << (space_avail - write_bits));
+            self.out_off += write_bits;
+            if (self.out_off == 5) {
+                if (i >= out.len) break;
+                out[i] = self.char();
+                i += 1;
+                self.out_off = 0;
+                self.buf = 0;
+            }
+        }
+        return i;
+    }
+
+    fn char(self: *const Self) u8 {
+        return self.buf + (if (self.buf < 26) @as(u8, 'A') else '2' - 26);
+    }
+};
+
+pub const DecodeError = error{CorruptInputError};
+
+pub const Decoder = struct {
+    const Self = @This();
+
+    out_off: u4 = 0,
+    buf: u8 = 0,
+
+    pub fn read(self: *Self, c: u8) DecodeError!?u8 {
+        var ret: ?u8 = null;
+        var decoded_c = try decodeChar(c);
+        var bits_left: u3 = 5;
+        while (bits_left > 0) {
+            var space_avail: u4 = 8 - self.out_off;
+            var write_bits: u3 = if (bits_left < space_avail) bits_left else @truncate(u3, space_avail);
+            bits_left -= write_bits;
+            var mask: u8 = (@as(u8, 0x01) << write_bits) - 1;
+            var want: u8 = (decoded_c >> bits_left) & mask;
+            self.buf |= want << @truncate(u3, space_avail - write_bits);
+            self.out_off += write_bits;
+            if (self.out_off == 8) {
+                ret = self.buf;
+                self.out_off = 0;
+                self.buf = 0;
+            }
+        }
+        return ret;
+    }
+
+    fn decodeChar(p: u8) DecodeError!u5 {
+        var value: u5 = 0;
+        if (p >= 'A' and p <= 'Z') {
+            value = @truncate(u5, p - @as(u8, 'A'));
+        } else if (p >= '2' and p <= '9') {
+            // '2' -> 26
+            value = @truncate(u5, p - @as(u8, '2') + 26);
+        } else {
+            return error.CorruptInputError;
+        }
+        return value;
+    }
+};
+
+pub fn encodedLen(src_len: usize) usize {
+    const src_len_bits = src_len * 8;
+    return src_len_bits / 5 + (if (src_len_bits % 5 > 0) @as(usize, 1) else 0);
+}
+
+pub fn decodedLen(enc_len: usize) usize {
+    const enc_len_bits = enc_len * 5;
+    return enc_len_bits / 8;
+}
+
+pub fn encode(bs: []const u8, out: []u8) usize {
+    var e = Encoder{};
+    var i: usize = 0;
+    for (bs) |b| {
+        if (i >= out.len) break;
+        i += e.write(b, out[i..]);
+    }
+    if (e.out_off != 0 and i < out.len) {
+        out[i] = e.char();
+        i += 1;
+    }
+    return i; // amount of bytes processed
+}
+
+pub fn decode(ps: []const u8, out: []u8) DecodeError!usize {
+    var d = Decoder{};
+    var i: usize = 0;
+    for (ps) |p| {
+        if (i >= out.len) break;
+        if (try d.read(p)) |b| {
+            out[i] = b;
+            i += 1;
+        }
+    }
+    if (d.out_off != 0 and i < out.len) {
+        out[i] = d.buf;
+        i += 1;
+    }
+    return i; // amount of bytes processed
+}
-- 
cgit v1.2.3