cjdenio/usps-barcode-decoder
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Caleb Denio
2025-05-27 18:07:49 -04:00
commit a7881f740a
8 changed files with 585 additions and 0 deletions
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src/imb.zig
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const std = @import("std");
const bar_positions = [_][4]u4{
.{ 7, 2, 4, 3 },
.{ 1, 10, 0, 0 },
.{ 9, 12, 2, 8 },
.{ 5, 5, 6, 11 },
.{ 8, 9, 3, 1 },
.{ 0, 1, 5, 12 },
.{ 2, 5, 1, 8 },
.{ 4, 4, 9, 11 },
.{ 6, 3, 8, 10 },
.{ 3, 9, 7, 6 },
.{ 5, 11, 1, 4 },
.{ 8, 5, 2, 12 },
.{ 9, 10, 0, 2 },
.{ 7, 1, 6, 7 },
.{ 3, 6, 4, 9 },
.{ 0, 3, 8, 6 },
.{ 6, 4, 2, 7 },
.{ 1, 1, 9, 9 },
.{ 7, 10, 5, 2 },
.{ 4, 0, 3, 8 },
.{ 6, 2, 0, 4 },
.{ 8, 11, 1, 0 },
.{ 9, 8, 3, 12 },
.{ 2, 6, 7, 7 },
.{ 5, 1, 4, 10 },
.{ 1, 12, 6, 9 },
.{ 7, 3, 8, 0 },
.{ 5, 8, 9, 7 },
.{ 4, 6, 2, 10 },
.{ 3, 4, 0, 5 },
.{ 8, 4, 5, 7 },
.{ 7, 11, 1, 9 },
.{ 6, 0, 9, 6 },
.{ 0, 6, 4, 8 },
.{ 2, 1, 3, 2 },
.{ 5, 9, 8, 12 },
.{ 4, 11, 6, 1 },
.{ 9, 5, 7, 4 },
.{ 3, 3, 1, 2 },
.{ 0, 7, 2, 0 },
.{ 1, 3, 4, 1 },
.{ 6, 10, 3, 5 },
.{ 8, 7, 9, 4 },
.{ 2, 11, 5, 6 },
.{ 0, 8, 7, 12 },
.{ 4, 2, 8, 1 },
.{ 5, 10, 3, 0 },
.{ 9, 3, 0, 9 },
.{ 6, 5, 2, 4 },
.{ 7, 8, 1, 7 },
.{ 5, 0, 4, 5 },
.{ 2, 3, 0, 10 },
.{ 6, 12, 9, 2 },
.{ 3, 11, 1, 6 },
.{ 8, 8, 7, 9 },
.{ 5, 4, 0, 11 },
.{ 1, 5, 2, 2 },
.{ 9, 1, 4, 12 },
.{ 8, 3, 6, 6 },
.{ 7, 0, 3, 7 },
.{ 4, 7, 7, 5 },
.{ 0, 12, 1, 11 },
.{ 2, 9, 9, 0 },
.{ 6, 8, 5, 3 },
.{ 3, 10, 8, 2 },
};
fn generateCharacterTable(n: u8, comptime len: usize) [len]u13 {
@setEvalBranchQuota(150000);
var table: [len]u13 = undefined;
var lower_index = 0;
var upper_index = len - 1;
for (0..0x2000) |i| {
const b = bitsSet(u13, i);
if (b != n) {
continue;
}
const reverse = @bitReverse(@as(u13, i));
if (reverse < i) {
continue;
}
if (reverse == i) {
table[upper_index] = i;
upper_index -= 1;
} else {
table[lower_index] = i;
lower_index += 1;
table[lower_index] = reverse;
lower_index += 1;
}
}
return table;
}
const character_table_5 = generateCharacterTable(5, 1287);
const character_table_2 = generateCharacterTable(2, 77);
const BarType = enum {
descending,
ascending,
tracking,
full,
};
pub const BarcodeResult = struct {
tracking_code: [20]u8,
routing_code: [11]u8,
};
pub const Error = error{
InvalidCharacter,
DecodingError,
InternalError,
InvalidChecksum,
};
fn bitsSet(comptime T: type, value: T) u8 {
var count: u8 = 0;
for (0..@typeInfo(T).int.bits) |i| {
count += @intCast((value >> @intCast(i)) & 1);
}
return count;
}
fn findCodeword(character: u13) u13 {
const b = bitsSet(u13, character);
if (b == 2) {
for (character_table_2, 0..) |item, codeword| {
if (character == item) {
return @intCast(codeword + 1287);
}
}
} else {
for (character_table_5, 0..) |item, codeword| {
if (character == item) {
return @intCast(codeword);
}
}
}
unreachable;
}
fn generateChecksum(data: [13]u8) u16 {
const generator_polynomial: u16 = 0x0F35;
var checksum: u16 = 0x07ff;
var byte: u16 = data[0] << 5;
for (2..8) |_| {
if (((checksum ^ byte) & 0x400) != 0) {
checksum = (checksum << 1) ^ generator_polynomial;
} else {
checksum <<= 1;
}
checksum &= 0x7FF;
byte <<= 1;
}
for (data[1..]) |b| {
byte = @as(u16, b) << 3;
for (0..8) |_| {
if (((checksum ^ byte) & 0x400) != 0) {
checksum = (checksum << 1) ^ generator_polynomial;
} else {
checksum <<= 1;
}
checksum &= 0x7FF;
byte <<= 1;
}
}
return checksum;
}
fn decode(bars: [65]BarType) Error!BarcodeResult {
var characters = [_]u13{0} ** 10;
for (bars, 0..) |bar, i| {
const positions = bar_positions[i];
if (bar == .descending or bar == .full) {
characters[positions[0]] |= (@as(u13, 1) << positions[1]);
}
if (bar == .ascending or bar == .full) {
characters[positions[2]] |= (@as(u13, 1) << positions[3]);
}
}
var checksum: u11 = 0;
for (&characters, 0..) |*character, i| {
switch (bitsSet(u13, character.*)) {
8, 11 => {
character.* ^= 0b1111111111111;
checksum |= (@as(u11, 1) << @intCast(i));
checksum |= (@as(u11, 1) << @intCast(i));
},
2, 5 => {},
else => return error.DecodingError,
}
character.* = findCodeword(character.*);
}
characters[9] /= 2;
if (characters[0] >= 659) {
characters[0] -= 659;
checksum |= 0b10000000000;
}
var bindata: u104 = 0;
bindata = @as(u104, characters[0]) * 1365 + characters[1];
bindata = bindata * 1365 + characters[2];
bindata = bindata * 1365 + characters[3];
bindata = bindata * 1365 + characters[4];
bindata = bindata * 1365 + characters[5];
bindata = bindata * 1365 + characters[6];
bindata = bindata * 1365 + characters[7];
bindata = bindata * 1365 + characters[8];
bindata = bindata * 636 + characters[9];
if (generateChecksum(@bitCast(@byteSwap(bindata))) != checksum) { // lol, only works on little-endian systems #WONTFIX
return error.InvalidChecksum;
}
var tracking_code: [20]u8 = undefined;
var routing_code = [_]u8{0} ** 11;
var i: u8 = 19;
while (i >= 2) : (i -= 1) {
tracking_code[i] = std.fmt.digitToChar(@intCast(bindata % 10), .lower);
bindata /= 10;
}
tracking_code[i] = std.fmt.digitToChar(@intCast(bindata % 5), .lower);
bindata /= 5;
i -= 1;
tracking_code[i] = std.fmt.digitToChar(@intCast(bindata % 10), .lower);
bindata /= 10;
switch (bindata) {
1...100000 => {
_ = std.fmt.bufPrint(&routing_code, "{d:05}", .{bindata - 1}) catch return error.InternalError;
},
100001...1000199999 => {
_ = std.fmt.bufPrint(&routing_code, "{d:09}", .{bindata - 100000 - 1}) catch return error.InternalError;
},
else => {
_ = std.fmt.bufPrint(&routing_code, "{d:011}", .{bindata - 1000000000 - 100000 - 1}) catch return error.InternalError;
},
}
return .{
.tracking_code = tracking_code,
.routing_code = routing_code,
};
}
pub fn decodeString(str: *const [65:0]u8) Error!BarcodeResult {
var bars: [65]BarType = undefined;
for (&bars, 0..) |*pt, i| {
pt.* = switch (str[i]) {
'A', 'a' => .ascending,
'D', 'd' => .descending,
'F', 'f' => .full,
'T', 't' => .tracking,
else => return error.InvalidCharacter,
};
}
const thing = try decode(bars);
return thing;
}
src/main.zig
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const std = @import("std");
const imb = @import("./imb.zig");
pub fn main() !void {
const stuff = try imb.decodeString("AADTFFDFTDADTAADAATFDTDDAAADDTDTTDAFADADDDTFFFDDTTTADFAAADFTDAADA");
std.log.info("{s}", .{stuff.tracking_code});
std.log.info("{s}", .{stuff.routing_code});
}
src/wasm.zig
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const std = @import("std");
const imb = @import("./imb.zig");
const allocator = std.heap.wasm_allocator;
export fn decodeStringWasm(str: *const [65:0]u8) usize {
if (imb.decodeString(str)) |v| {
const ptr = allocator.create([31]u8) catch unreachable;
const result = v.tracking_code ++ v.routing_code;
@memcpy(ptr, &result);
return @intFromPtr(ptr);
} else |e| switch (e) {
error.InvalidCharacter => return 0,
error.DecodingError => return 1,
error.InternalError => return 2,
error.InvalidChecksum => return 3,
}
}
export fn malloc(len: u8) [*]u8 {
return (allocator.alloc(u8, len) catch unreachable).ptr;
}
export fn free(ptr: [*]u8, len: u8) void {
allocator.free(ptr[0..len]);
}