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Merge pull request #5588 from tgschultz/leb128-output
LEB128 overhaul and output
This commit is contained in:
Andrew Kelley
GitHub
commit
e820678ca1
@ -1,171 +1,211 @@
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const std = @import("std");
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const testing = std.testing;
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pub fn readULEB128(comptime T: type, in_stream: var) !T {
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const ShiftT = std.meta.Int(false, std.math.log2(T.bit_count));
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/// Read a single unsigned LEB128 value from the given reader as type T,
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/// or error.Overflow if the value cannot fit.
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pub fn readULEB128(comptime T: type, reader: var) !T {
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const U = if (T.bit_count < 8) u8 else T;
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const ShiftT = std.math.Log2Int(U);
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var result: T = 0;
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var shift: usize = 0;
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const max_group = (U.bit_count + 6) / 7;
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var value = @as(U, 0);
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var group = @as(ShiftT, 0);
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while (group < max_group) : (group += 1) {
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const byte = try reader.readByte();
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var temp = @as(U, byte & 0x7f);
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if (@shlWithOverflow(U, temp, group * 7, &temp)) return error.Overflow;
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value |= temp;
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if (byte & 0x80 == 0) break;
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} else {
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return error.Overflow;
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}
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// only applies in the case that we extended to u8
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if (U != T) {
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if (value > std.math.maxInt(T)) return error.Overflow;
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}
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return @truncate(T, value);
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}
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/// Write a single unsigned integer as unsigned LEB128 to the given writer.
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pub fn writeULEB128(writer: var, uint_value: var) !void {
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const T = @TypeOf(uint_value);
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const U = if (T.bit_count < 8) u8 else T;
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var value = @intCast(U, uint_value);
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while (true) {
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const byte = try in_stream.readByte();
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if (shift > T.bit_count)
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return error.Overflow;
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var operand: T = undefined;
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if (@shlWithOverflow(T, byte & 0x7f, @intCast(ShiftT, shift), &operand))
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return error.Overflow;
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result |= operand;
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if ((byte & 0x80) == 0)
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return result;
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shift += 7;
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const byte = @truncate(u8, value & 0x7f);
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value >>= 7;
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if (value == 0) {
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try writer.writeByte(byte);
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break;
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} else {
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try writer.writeByte(byte | 0x80);
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}
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}
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}
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pub fn readULEB128Mem(comptime T: type, ptr: *[*]const u8) !T {
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const ShiftT = std.meta.Int(false, std.math.log2(T.bit_count));
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/// Read a single unsinged integer from the given memory as type T.
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/// The provided slice reference will be updated to point to the byte after the last byte read.
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pub fn readULEB128Mem(comptime T: type, ptr: *[]const u8) !T {
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var buf = std.io.fixedBufferStream(ptr.*);
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const value = try readULEB128(T, buf.reader());
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ptr.*.ptr += buf.pos;
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return value;
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}
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var result: T = 0;
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var shift: usize = 0;
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var i: usize = 0;
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/// Write a single unsigned LEB128 integer to the given memory as unsigned LEB128,
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/// returning the number of bytes written.
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pub fn writeULEB128Mem(ptr: []u8, uint_value: var) !usize {
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const T = @TypeOf(uint_value);
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const max_group = (T.bit_count + 6) / 7;
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var buf = std.io.fixedBufferStream(ptr);
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try writeULEB128(buf.writer(), uint_value);
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return buf.pos;
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}
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while (true) : (i += 1) {
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const byte = ptr.*[i];
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/// Read a single signed LEB128 value from the given reader as type T,
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/// or error.Overflow if the value cannot fit.
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pub fn readILEB128(comptime T: type, reader: var) !T {
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const S = if (T.bit_count < 8) i8 else T;
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const U = std.meta.Int(false, S.bit_count);
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const ShiftU = std.math.Log2Int(U);
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if (shift > T.bit_count)
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return error.Overflow;
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const max_group = (U.bit_count + 6) / 7;
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var operand: T = undefined;
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if (@shlWithOverflow(T, byte & 0x7f, @intCast(ShiftT, shift), &operand))
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return error.Overflow;
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var value = @as(U, 0);
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var group = @as(ShiftU, 0);
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result |= operand;
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while (group < max_group) : (group += 1) {
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const byte = try reader.readByte();
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var temp = @as(U, byte & 0x7f);
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if ((byte & 0x80) == 0) {
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ptr.* += i + 1;
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return result;
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const shift = group * 7;
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if (@shlWithOverflow(U, temp, shift, &temp)) {
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// Overflow is ok so long as the sign bit is set and this is the last byte
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if (byte & 0x80 != 0) return error.Overflow;
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if (@bitCast(S, temp) >= 0) return error.Overflow;
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// and all the overflowed bits are 1
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const remaining_shift = @intCast(u3, U.bit_count - @as(u16, shift));
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const remaining_bits = @bitCast(i8, byte | 0x80) >> remaining_shift;
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if (remaining_bits != -1) return error.Overflow;
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}
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shift += 7;
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value |= temp;
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if (byte & 0x80 == 0) {
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const needs_sign_ext = group + 1 < max_group;
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if (byte & 0x40 != 0 and needs_sign_ext) {
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const ones = @as(S, -1);
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value |= @bitCast(U, ones) << (shift + 7);
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}
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break;
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}
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} else {
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return error.Overflow;
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}
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const result = @bitCast(S, value);
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// Only applies if we extended to i8
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if (S != T) {
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if (result > std.math.maxInt(T) or result < std.math.minInt(T)) return error.Overflow;
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}
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return @truncate(T, result);
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}
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pub fn readILEB128(comptime T: type, in_stream: var) !T {
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const UT = std.meta.Int(false, T.bit_count);
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const ShiftT = std.meta.Int(false, std.math.log2(T.bit_count));
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/// Write a single signed integer as signed LEB128 to the given writer.
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pub fn writeILEB128(writer: var, int_value: var) !void {
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const T = @TypeOf(int_value);
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const S = if (T.bit_count < 8) i8 else T;
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const U = std.meta.Int(false, S.bit_count);
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var result: UT = 0;
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var shift: usize = 0;
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var value = @intCast(S, int_value);
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while (true) {
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const byte: u8 = try in_stream.readByte();
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if (shift > T.bit_count)
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return error.Overflow;
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var operand: UT = undefined;
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if (@shlWithOverflow(UT, @as(UT, byte & 0x7f), @intCast(ShiftT, shift), &operand)) {
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if (byte != 0x7f)
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return error.Overflow;
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}
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result |= operand;
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shift += 7;
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if ((byte & 0x80) == 0) {
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if (shift < T.bit_count and (byte & 0x40) != 0) {
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result |= @bitCast(UT, @intCast(T, -1)) << @intCast(ShiftT, shift);
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}
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return @bitCast(T, result);
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const uvalue = @bitCast(U, value);
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const byte = @truncate(u8, uvalue);
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value >>= 6;
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if (value == -1 or value == 0) {
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try writer.writeByte(byte & 0x7F);
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break;
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} else {
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value >>= 1;
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try writer.writeByte(byte | 0x80);
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}
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}
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}
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pub fn readILEB128Mem(comptime T: type, ptr: *[*]const u8) !T {
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const UT = std.meta.Int(false, T.bit_count);
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const ShiftT = std.meta.Int(false, std.math.log2(T.bit_count));
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var result: UT = 0;
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var shift: usize = 0;
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var i: usize = 0;
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while (true) : (i += 1) {
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const byte = ptr.*[i];
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if (shift > T.bit_count)
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return error.Overflow;
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var operand: UT = undefined;
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if (@shlWithOverflow(UT, @as(UT, byte & 0x7f), @intCast(ShiftT, shift), &operand)) {
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if (byte != 0x7f)
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return error.Overflow;
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}
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result |= operand;
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shift += 7;
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if ((byte & 0x80) == 0) {
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if (shift < T.bit_count and (byte & 0x40) != 0) {
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result |= @bitCast(UT, @intCast(T, -1)) << @intCast(ShiftT, shift);
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}
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ptr.* += i + 1;
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return @bitCast(T, result);
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}
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}
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/// Read a single singed LEB128 integer from the given memory as type T.
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/// The provided slice reference will be updated to point to the byte after the last byte read.
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pub fn readILEB128Mem(comptime T: type, ptr: *[]const u8) !T {
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var buf = std.io.fixedBufferStream(ptr.*);
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const value = try readILEB128(T, buf.reader());
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ptr.*.ptr += buf.pos;
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return value;
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}
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/// Write a single signed LEB128 integer to the given memory as unsigned LEB128,
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/// returning the number of bytes written.
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pub fn writeILEB128Mem(ptr: []u8, int_value: var) !usize {
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const T = @TypeOf(int_value);
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var buf = std.io.fixedBufferStream(ptr);
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try writeILEB128(buf.writer(), int_value);
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return buf.pos;
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}
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// tests
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fn test_read_stream_ileb128(comptime T: type, encoded: []const u8) !T {
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var in_stream = std.io.fixedBufferStream(encoded);
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return try readILEB128(T, in_stream.inStream());
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var reader = std.io.fixedBufferStream(encoded);
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return try readILEB128(T, reader.reader());
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}
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fn test_read_stream_uleb128(comptime T: type, encoded: []const u8) !T {
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var in_stream = std.io.fixedBufferStream(encoded);
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return try readULEB128(T, in_stream.inStream());
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var reader = std.io.fixedBufferStream(encoded);
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return try readULEB128(T, reader.reader());
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}
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fn test_read_ileb128(comptime T: type, encoded: []const u8) !T {
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var in_stream = std.io.fixedBufferStream(encoded);
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const v1 = readILEB128(T, in_stream.inStream());
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var in_ptr = encoded.ptr;
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const v2 = readILEB128Mem(T, &in_ptr);
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var reader = std.io.fixedBufferStream(encoded);
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const v1 = try readILEB128(T, reader.reader());
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var in_ptr = encoded;
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const v2 = try readILEB128Mem(T, &in_ptr);
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testing.expectEqual(v1, v2);
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return v1;
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}
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fn test_read_uleb128(comptime T: type, encoded: []const u8) !T {
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var in_stream = std.io.fixedBufferStream(encoded);
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const v1 = readULEB128(T, in_stream.inStream());
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var in_ptr = encoded.ptr;
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const v2 = readULEB128Mem(T, &in_ptr);
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var reader = std.io.fixedBufferStream(encoded);
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const v1 = try readULEB128(T, reader.reader());
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var in_ptr = encoded;
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const v2 = try readULEB128Mem(T, &in_ptr);
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testing.expectEqual(v1, v2);
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return v1;
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}
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fn test_read_ileb128_seq(comptime T: type, comptime N: usize, encoded: []const u8) void {
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var in_stream = std.io.fixedBufferStream(encoded);
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var in_ptr = encoded.ptr;
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fn test_read_ileb128_seq(comptime T: type, comptime N: usize, encoded: []const u8) !void {
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var reader = std.io.fixedBufferStream(encoded);
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var in_ptr = encoded;
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var i: usize = 0;
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while (i < N) : (i += 1) {
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const v1 = readILEB128(T, in_stream.inStream());
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const v2 = readILEB128Mem(T, &in_ptr);
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const v1 = try readILEB128(T, reader.reader());
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const v2 = try readILEB128Mem(T, &in_ptr);
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testing.expectEqual(v1, v2);
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}
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}
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fn test_read_uleb128_seq(comptime T: type, comptime N: usize, encoded: []const u8) void {
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var in_stream = std.io.fixedBufferStream(encoded);
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var in_ptr = encoded.ptr;
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fn test_read_uleb128_seq(comptime T: type, comptime N: usize, encoded: []const u8) !void {
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var reader = std.io.fixedBufferStream(encoded);
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var in_ptr = encoded;
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var i: usize = 0;
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while (i < N) : (i += 1) {
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const v1 = readULEB128(T, in_stream.inStream());
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const v2 = readULEB128Mem(T, &in_ptr);
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const v1 = try readULEB128(T, reader.reader());
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const v2 = try readULEB128Mem(T, &in_ptr);
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testing.expectEqual(v1, v2);
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}
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}
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@ -212,7 +252,7 @@ test "deserialize signed LEB128" {
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testing.expect((try test_read_ileb128(i64, "\x80\x81\x80\x00")) == 0x80);
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// Decode sequence of SLEB128 values
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test_read_ileb128_seq(i64, 4, "\x81\x01\x3f\x80\x7f\x80\x80\x80\x00");
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try test_read_ileb128_seq(i64, 4, "\x81\x01\x3f\x80\x7f\x80\x80\x80\x00");
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}
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test "deserialize unsigned LEB128" {
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@ -252,5 +292,99 @@ test "deserialize unsigned LEB128" {
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testing.expect((try test_read_uleb128(u64, "\x80\x81\x80\x00")) == 0x80);
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// Decode sequence of ULEB128 values
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test_read_uleb128_seq(u64, 4, "\x81\x01\x3f\x80\x7f\x80\x80\x80\x00");
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try test_read_uleb128_seq(u64, 4, "\x81\x01\x3f\x80\x7f\x80\x80\x80\x00");
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}
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fn test_write_leb128(value: var) !void {
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const T = @TypeOf(value);
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const writeStream = if (T.is_signed) writeILEB128 else writeULEB128;
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const writeMem = if (T.is_signed) writeILEB128Mem else writeULEB128Mem;
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const readStream = if (T.is_signed) readILEB128 else readULEB128;
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const readMem = if (T.is_signed) readILEB128Mem else readULEB128Mem;
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// decode to a larger bit size too, to ensure sign extension
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// is working as expected
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const larger_type_bits = ((T.bit_count + 8) / 8) * 8;
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const B = std.meta.Int(T.is_signed, larger_type_bits);
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const bytes_needed = bn: {
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const S = std.meta.Int(T.is_signed, @sizeOf(T) * 8);
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if (T.bit_count <= 7) break :bn @as(u16, 1);
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const unused_bits = if (value < 0) @clz(T, ~value) else @clz(T, value);
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const used_bits: u16 = (T.bit_count - unused_bits) + @boolToInt(T.is_signed);
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if (used_bits <= 7) break :bn @as(u16, 1);
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break :bn ((used_bits + 6) / 7);
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};
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const max_groups = if (T.bit_count == 0) 1 else (T.bit_count + 6) / 7;
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var buf: [max_groups]u8 = undefined;
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var fbs = std.io.fixedBufferStream(&buf);
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// stream write
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try writeStream(fbs.writer(), value);
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const w1_pos = fbs.pos;
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testing.expect(w1_pos == bytes_needed);
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// stream read
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fbs.pos = 0;
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const sr = try readStream(T, fbs.reader());
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testing.expect(fbs.pos == w1_pos);
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testing.expect(sr == value);
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// bigger type stream read
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fbs.pos = 0;
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const bsr = try readStream(B, fbs.reader());
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testing.expect(fbs.pos == w1_pos);
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testing.expect(bsr == value);
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// mem write
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const w2_pos = try writeMem(&buf, value);
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testing.expect(w2_pos == w1_pos);
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// mem read
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var buf_ref: []u8 = buf[0..];
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const mr = try readMem(T, &buf_ref);
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testing.expect(@ptrToInt(buf_ref.ptr) - @ptrToInt(&buf) == w2_pos);
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testing.expect(mr == value);
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// bigger type mem read
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buf_ref = buf[0..];
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const bmr = try readMem(T, &buf_ref);
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testing.expect(@ptrToInt(buf_ref.ptr) - @ptrToInt(&buf) == w2_pos);
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testing.expect(bmr == value);
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}
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test "serialize unsigned LEB128" {
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const max_bits = 18;
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comptime var t = 0;
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inline while (t <= max_bits) : (t += 1) {
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const T = std.meta.Int(false, t);
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const min = std.math.minInt(T);
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const max = std.math.maxInt(T);
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var i = @as(std.meta.Int(false, T.bit_count + 1), min);
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while (i <= max) : (i += 1) try test_write_leb128(@intCast(T, i));
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}
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}
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test "serialize signed LEB128" {
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// explicitly test i0 because starting `t` at 0
|
||||
// will break the while loop
|
||||
try test_write_leb128(@as(i0, 0));
|
||||
|
||||
const max_bits = 18;
|
||||
|
||||
comptime var t = 1;
|
||||
inline while (t <= max_bits) : (t += 1) {
|
||||
const T = std.meta.Int(true, t);
|
||||
const min = std.math.minInt(T);
|
||||
const max = std.math.maxInt(T);
|
||||
var i = @as(std.meta.Int(true, T.bit_count + 1), min);
|
||||
|
||||
while (i <= max) : (i += 1) try test_write_leb128(@intCast(T, i));
|
||||
}
|
||||
}
|
||||
|
||||
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Reference in New Issue
Block a user