tiny.filigree.layout.coverage

1const std = @import("std");23const binary = @import("binary.zig");4const LayoutError = binary.LayoutError;5const hasBytes = binary.hasBytes;6const readU16 = binary.readU16;78pub const Coverage = union(enum) {9    format_1: CoverageFormat1,10    format_2: CoverageFormat2,1112    pub fn init(data: []const u8, offset: usize) LayoutError!Coverage {13        if (!hasBytes(data, offset, 2)) return error.InvalidLayout;14        return switch (try readU16(data, offset)) {15            1 => .{ .format_1 = try CoverageFormat1.init(data, offset) },16            2 => .{ .format_2 = try CoverageFormat2.init(data, offset) },17            else => error.UnsupportedCoverage,18        };19    }2021    pub fn index(self: Coverage, data: []const u8, glyph_id: u32) LayoutError!?u16 {22        return switch (self) {23            .format_1 => |format| format.index(data, glyph_id),24            .format_2 => |format| format.index(data, glyph_id),25        };26    }27};2829pub const CoverageFormat1 = struct {30    glyph_array_offset: usize,31    glyph_count: u16,3233    fn init(data: []const u8, offset: usize) LayoutError!CoverageFormat1 {34        if (!hasBytes(data, offset, 4)) return error.InvalidLayout;35        const glyph_count = try readU16(data, offset + 2);36        const array_offset = offset + 4;37        const array_len = @as(usize, glyph_count) * 2;38        if (!hasBytes(data, array_offset, array_len)) return error.InvalidLayout;39        var previous: ?u16 = null;40        for (0..glyph_count) |i| {41            const glyph = try readU16(data, array_offset + i * 2);42            if (previous) |seen| {43                if (glyph <= seen) return error.InvalidLayout;44            }45            previous = glyph;46        }47        return .{48            .glyph_array_offset = array_offset,49            .glyph_count = glyph_count,50        };51    }5253    fn index(self: CoverageFormat1, data: []const u8, glyph_id: u32) LayoutError!?u16 {54        if (glyph_id > std.math.maxInt(u16)) return null;55        const glyph: u16 = @intCast(glyph_id);56        var left: usize = 0;57        var right: usize = self.glyph_count;58        while (left < right) {59            const mid = left + (right - left) / 2;60            const candidate = try readU16(data, self.glyph_array_offset + mid * 2);61            if (glyph < candidate) {62                right = mid;63            } else if (glyph > candidate) {64                left = mid + 1;65            } else {66                return @intCast(mid);67            }68        }69        return null;70    }71};7273pub const CoverageFormat2 = struct {74    range_array_offset: usize,75    range_count: u16,7677    fn init(data: []const u8, offset: usize) LayoutError!CoverageFormat2 {78        if (!hasBytes(data, offset, 4)) return error.InvalidLayout;79        const range_count = try readU16(data, offset + 2);80        const array_offset = offset + 4;81        const array_len = @as(usize, range_count) * 6;82        if (!hasBytes(data, array_offset, array_len)) return error.InvalidLayout;83        var previous_end: ?u16 = null;84        for (0..range_count) |i| {85            const record = array_offset + i * 6;86            const start = try readU16(data, record);87            const end = try readU16(data, record + 2);88            if (start > end) return error.InvalidLayout;89            if (previous_end) |seen| {90                if (start <= seen) return error.InvalidLayout;91            }92            previous_end = end;93        }94        return .{95            .range_array_offset = array_offset,96            .range_count = range_count,97        };98    }99100    fn index(self: CoverageFormat2, data: []const u8, glyph_id: u32) LayoutError!?u16 {101        if (glyph_id > std.math.maxInt(u16)) return null;102        const glyph: u16 = @intCast(glyph_id);103        var left: usize = 0;104        var right: usize = self.range_count;105        while (left < right) {106            const mid = left + (right - left) / 2;107            const record = self.range_array_offset + mid * 6;108            const start = try readU16(data, record);109            const end = try readU16(data, record + 2);110            if (glyph < start) {111                right = mid;112            } else if (glyph > end) {113                left = mid + 1;114            } else {115                const start_index = try readU16(data, record + 4);116                const delta = glyph - start;117                if (start_index > std.math.maxInt(u16) - delta) return error.InvalidLayout;118                return start_index + delta;119            }120        }121        return null;122    }123};124125test "Coverage format 1 maps sorted glyph array to indexes" {126    const data = [_]u8{127        0, 1,128        0, 3,129        0, 5,130        0, 9,131        0, 20,132    };133    const coverage = try Coverage.init(&data, 0);134    try std.testing.expectEqual(@as(?u16, 0), try coverage.index(&data, 5));135    try std.testing.expectEqual(@as(?u16, 1), try coverage.index(&data, 9));136    try std.testing.expectEqual(@as(?u16, 2), try coverage.index(&data, 20));137    try std.testing.expectEqual(@as(?u16, null), try coverage.index(&data, 6));138    try std.testing.expectEqual(@as(?u16, null), try coverage.index(&data, 0x1_0000));139}140141test "Coverage format 1 rejects unsorted glyph array" {142    const data = [_]u8{143        0, 1,144        0, 2,145        0, 7,146        0, 7,147    };148    try std.testing.expectError(error.InvalidLayout, Coverage.init(&data, 0));149}150151test "Coverage format 2 maps glyph ranges to indexes" {152    const data = [_]u8{153        0, 2,154        0, 2,155        0, 10,156        0, 12,157        0, 0,158        0, 20,159        0, 21,160        0, 3,161    };162    const coverage = try Coverage.init(&data, 0);163    try std.testing.expectEqual(@as(?u16, 0), try coverage.index(&data, 10));164    try std.testing.expectEqual(@as(?u16, 2), try coverage.index(&data, 12));165    try std.testing.expectEqual(@as(?u16, 3), try coverage.index(&data, 20));166    try std.testing.expectEqual(@as(?u16, 4), try coverage.index(&data, 21));167    try std.testing.expectEqual(@as(?u16, null), try coverage.index(&data, 13));168}169170test "Coverage format 2 rejects overlapping ranges" {171    const data = [_]u8{172        0, 2,173        0, 2,174        0, 10,175        0, 12,176        0, 0,177        0, 12,178        0, 14,179        0, 3,180    };181    try std.testing.expectError(error.InvalidLayout, Coverage.init(&data, 0));182}183184test "Coverage honors nonzero table offsets" {185    const data = [_]u8{186        0xaa, 0xbb,187        0,    1,188        0,    1,189        0,    42,190    };191    const coverage = try Coverage.init(&data, 2);192    try std.testing.expectEqual(@as(?u16, 0), try coverage.index(&data, 42));193}

1pub const coverage = @import("coverage.zig");