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Added test to ensure minimum number of bytes is emitted for writes

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tgschultz 2020-06-16 16:11:39 +00:00
parent a0160d776f
commit 38e69a9e6a
1 changed files with 33 additions and 22 deletions
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55
lib/std/debug/leb128.zig
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@ -1,7 +1,7 @@
const std = @import("std");
const testing = std.testing;
///Read a single unsigned LEB128 value from the given reader as type T,
/// Read a single unsigned LEB128 value from the given reader as type T,
/// or error.Overflow if the value cannot fit.
pub fn readULEB128(comptime T: type, reader: var) !T {
const U = if (T.bit_count < 8) u8 else T;
@ -24,7 +24,7 @@ pub fn readULEB128(comptime T: type, reader: var) !T {
return error.Overflow;
}
//only applies in the case that we extended to u8
// only applies in the case that we extended to u8
if (U != T) {
if (value > std.math.maxInt(T)) return error.Overflow;
}
@ -32,7 +32,7 @@ pub fn readULEB128(comptime T: type, reader: var) !T {
return @truncate(T, value);
}
///Write a single unsigned integer as unsigned LEB128 to the given writer.
/// Write a single unsigned integer as unsigned LEB128 to the given writer.
pub fn writeULEB128(writer: var, uint_value: var) !void {
const T = @TypeOf(uint_value);
const U = if (T.bit_count < 8) u8 else T;
@ -50,7 +50,7 @@ pub fn writeULEB128(writer: var, uint_value: var) !void {
}
}
///Read a single unsinged integer from the given memory as type T.
/// Read a single unsinged integer from the given memory as type T.
/// The provided slice reference will be updated to point to the byte after the last byte read.
pub fn readULEB128Mem(comptime T: type, ptr: *[]const u8) !T {
var buf = std.io.fixedBufferStream(ptr.*);
@ -59,7 +59,7 @@ pub fn readULEB128Mem(comptime T: type, ptr: *[]const u8) !T {
return value;
}
///Write a single unsigned LEB128 integer to the given memory as unsigned LEB128,
/// Write a single unsigned LEB128 integer to the given memory as unsigned LEB128,
/// returning the number of bytes written.
pub fn writeULEB128Mem(ptr: []u8, uint_value: var) !usize {
const T = @TypeOf(uint_value);
@ -69,7 +69,7 @@ pub fn writeULEB128Mem(ptr: []u8, uint_value: var) !usize {
return buf.pos;
}
///Read a single signed LEB128 value from the given reader as type T,
/// Read a single signed LEB128 value from the given reader as type T,
/// or error.Overflow if the value cannot fit.
pub fn readILEB128(comptime T: type, reader: var) !T {
const S = if (T.bit_count < 8) i8 else T;
@ -87,11 +87,11 @@ pub fn readILEB128(comptime T: type, reader: var) !T {
const shift = group * 7;
if (@shlWithOverflow(U, temp, shift, &temp)) {
//Overflow is ok so long as the sign bit is set and this is the last byte
// Overflow is ok so long as the sign bit is set and this is the last byte
if (byte & 0x80 != 0) return error.Overflow;
if (@bitCast(S, temp) >= 0) return error.Overflow;
//and all the overflowed bits are 1
// and all the overflowed bits are 1
const remaining_shift = @intCast(u3, U.bit_count - @as(u16, shift));
const remaining_bits = @bitCast(i8, byte | 0x80) >> remaining_shift;
if (remaining_bits != -1) return error.Overflow;
@ -111,7 +111,7 @@ pub fn readILEB128(comptime T: type, reader: var) !T {
}
const result = @bitCast(S, value);
//Only applies if we extended to i8
// Only applies if we extended to i8
if (S != T) {
if (result > std.math.maxInt(T) or result < std.math.minInt(T)) return error.Overflow;
}
@ -119,7 +119,7 @@ pub fn readILEB128(comptime T: type, reader: var) !T {
return @truncate(T, result);
}
///Write a single signed integer as signed LEB128 to the given writer.
/// Write a single signed integer as signed LEB128 to the given writer.
pub fn writeILEB128(writer: var, int_value: var) !void {
const T = @TypeOf(int_value);
const S = if (T.bit_count < 8) i8 else T;
@ -141,7 +141,7 @@ pub fn writeILEB128(writer: var, int_value: var) !void {
}
}
///Read a single singed LEB128 integer from the given memory as type T.
/// Read a single singed LEB128 integer from the given memory as type T.
/// The provided slice reference will be updated to point to the byte after the last byte read.
pub fn readILEB128Mem(comptime T: type, ptr: *[]const u8) !T {
var buf = std.io.fixedBufferStream(ptr.*);
@ -150,7 +150,7 @@ pub fn readILEB128Mem(comptime T: type, ptr: *[]const u8) !T {
return value;
}
///Write a single signed LEB128 integer to the given memory as unsigned LEB128,
/// Write a single signed LEB128 integer to the given memory as unsigned LEB128,
/// returning the number of bytes written.
pub fn writeILEB128Mem(ptr: []u8, int_value: var) !usize {
const T = @TypeOf(int_value);
@ -159,7 +159,7 @@ pub fn writeILEB128Mem(ptr: []u8, int_value: var) !usize {
return buf.pos;
}
//tests
// tests
fn test_read_stream_ileb128(comptime T: type, encoded: []const u8) !T {
var reader = std.io.fixedBufferStream(encoded);
return try readILEB128(T, reader.reader());
@ -303,43 +303,54 @@ fn test_write_leb128(value: var) !void {
const readStream = if (T.is_signed) readILEB128 else readULEB128;
const readMem = if (T.is_signed) readILEB128Mem else readULEB128Mem;
//decode to a larger bit size too, to ensure sign extension
// decode to a larger bit size too, to ensure sign extension
// is working as expected
const larger_type_bits = ((T.bit_count + 8) / 8) * 8;
const B = std.meta.Int(T.is_signed, larger_type_bits);
const bytes_needed = bn: {
const S = std.meta.Int(T.is_signed, @sizeOf(T) * 8);
if (T.bit_count <= 7) break :bn @as(u16, 1);
const unused_bits = if (value < 0) @clz(T, ~value) else @clz(T, value);
const used_bits: u16 = (T.bit_count - unused_bits) + @boolToInt(T.is_signed);
if (used_bits <= 7) break :bn @as(u16, 1);
break :bn ((used_bits + 6) / 7);
};
const max_groups = if (T.bit_count == 0) 1 else (T.bit_count + 6) / 7;
var buf: [max_groups]u8 = undefined;
var fbs = std.io.fixedBufferStream(&buf);
//stream write
// stream write
try writeStream(fbs.writer(), value);
const w1_pos = fbs.pos;
testing.expect(w1_pos > 0);
testing.expect(w1_pos == bytes_needed);
//stream read
// stream read
fbs.pos = 0;
const sr = try readStream(T, fbs.reader());
testing.expect(fbs.pos == w1_pos);
testing.expect(sr == value);
//bigger type stream read
// bigger type stream read
fbs.pos = 0;
const bsr = try readStream(B, fbs.reader());
testing.expect(fbs.pos == w1_pos);
testing.expect(bsr == value);
//mem write
// mem write
const w2_pos = try writeMem(&buf, value);
testing.expect(w2_pos == w1_pos);
//mem read
// mem read
var buf_ref: []u8 = buf[0..];
const mr = try readMem(T, &buf_ref);
testing.expect(@ptrToInt(buf_ref.ptr) - @ptrToInt(&buf) == w2_pos);
testing.expect(mr == value);
//bigger type mem read
// bigger type mem read
buf_ref = buf[0..];
const bmr = try readMem(T, &buf_ref);
testing.expect(@ptrToInt(buf_ref.ptr) - @ptrToInt(&buf) == w2_pos);
@ -361,7 +372,7 @@ test "serialize unsigned LEB128" {
}
test "serialize signed LEB128" {
//explicitly test i0 because starting `t` at 0
// explicitly test i0 because starting `t` at 0
// will break the while loop
try test_write_leb128(@as(i0, 0));