tiny.pdf.FilterPredictor

1pub const Predictor = struct {2    predictor: u32 = 1,3    colors: u32 = 1,4    bits: u32 = 8,5    columns: u32 = 1,67    pub fn fromDict(dict: object.Dict) DecodeError!Predictor {8        return .{9            .predictor = try directUnsigned(dict, "Predictor", 1),10            .colors = try directUnsigned(dict, "Colors", 1),11            .bits = try directUnsigned(dict, "BitsPerComponent", 8),12            .columns = try directUnsigned(dict, "Columns", 1),13        };14    }1516    pub fn rowLength(self: Predictor) DecodeError!usize {17        if (self.columns == 0 or self.colors == 0) return error.DecodeFailed;18        const valid_bits = self.bits == 1 or self.bits == 2 or self.bits == 4 or19            self.bits == 8 or self.bits == 16;20        if (!valid_bits) return error.DecodeFailed;21        const channel_bits = std.math.mul(u64, self.colors, self.bits) catch22            return error.DecodeFailed;23        const row_bits = std.math.mul(u64, self.columns, channel_bits) catch24            return error.DecodeFailed;25        return std.math.cast(usize, (row_bits + 7) / 8) orelse error.DecodeFailed;26    }2728    pub fn sampleLength(self: Predictor) DecodeError!usize {29        const sample_bits = std.math.mul(u64, self.colors, self.bits) catch30            return error.DecodeFailed;31        const bytes = std.math.cast(usize, (sample_bits + 7) / 8) orelse32            return error.DecodeFailed;33        return @max(1, bytes);34    }3536    fn directUnsigned(dict: object.Dict, key: []const u8, default: u32) DecodeError!u32 {37        const value = dict.get(key) orelse return default;38        return switch (value) {39            .integer => |raw| if (raw >= 0 and raw <= std.math.maxInt(u32))40                @intCast(raw)41            else42                error.UnsupportedFilter,43            else => error.UnsupportedFilter,44        };45    }46};

1pub const FilterPredictor = filter.Predictor;