Commit 7b72fc6bbc
Changed files (3)
lib
std
math
src
lib/std/math/big/int.zig
@@ -1624,18 +1624,16 @@ pub const Mutable = struct {
}
/// Read the value of `x` from `buffer`
- /// Asserts that `buffer` and `bit_count` are large enough to store the value.
+ /// Asserts that `buffer`, `abi_size`, and `bit_count` are large enough to store the value.
///
- /// For integers with a well-defined layout (e.g. all power-of-two integers), this function
- /// reads from `buffer` as if it were the contents of @ptrCast([]const u8, &x), where the
- /// slice length is taken to be @sizeOf(std.meta.Int(signedness, <bit_count>))
- ///
- /// For integers with a non-well-defined layout, `buffer` must have been created by
- /// writeTwosComplement.
+ /// The contents of `buffer` are interpreted as if they were the contents of
+ /// @ptrCast(*[abi_size]const u8, &x). Byte ordering is determined by `endian`
+ /// and any required padding bits are expected on the MSB end.
pub fn readTwosComplement(
x: *Mutable,
buffer: []const u8,
bit_count: usize,
+ abi_size: usize,
endian: Endian,
signedness: Signedness,
) void {
@@ -1646,20 +1644,18 @@ pub const Mutable = struct {
return;
}
- // byte_count is the total amount of bytes to read from buffer
- var byte_count = @sizeOf(Limb) * (bit_count / @bitSizeOf(Limb));
- if (bit_count % @bitSizeOf(Limb) != 0) { // Round up to a power-of-two integer <= Limb
- byte_count += (std.math.ceilPowerOfTwoAssert(usize, bit_count % @bitSizeOf(Limb)) + 7) / 8;
- }
-
- const limb_count = calcTwosCompLimbCount(8 * byte_count);
+ // byte_count is our total read size: it cannot exceed abi_size,
+ // but may be less as long as it includes the required bits
+ const limb_count = calcTwosCompLimbCount(bit_count);
+ const byte_count = std.math.min(abi_size, @sizeOf(Limb) * limb_count);
+ assert(8 * byte_count >= bit_count);
// Check whether the input is negative
var positive = true;
if (signedness == .signed) {
var last_byte = switch (endian) {
.Little => ((bit_count + 7) / 8) - 1,
- .Big => byte_count - ((bit_count + 7) / 8),
+ .Big => abi_size - ((bit_count + 7) / 8),
};
const sign_bit = @as(u8, 1) << @intCast(u3, (bit_count - 1) % 8);
@@ -1672,7 +1668,7 @@ pub const Mutable = struct {
while (limb_index < bit_count / @bitSizeOf(Limb)) : (limb_index += 1) {
var buf_index = switch (endian) {
.Little => @sizeOf(Limb) * limb_index,
- .Big => byte_count - (limb_index + 1) * @sizeOf(Limb),
+ .Big => abi_size - (limb_index + 1) * @sizeOf(Limb),
};
const limb_buf = @ptrCast(*const [@sizeOf(Limb)]u8, buffer[buf_index..]);
@@ -1683,32 +1679,34 @@ pub const Mutable = struct {
x.limbs[limb_index] = limb;
}
- // Copy any remaining bytes, using the nearest power-of-two integer that is large enough
- const bits_left = @intCast(Log2Limb, bit_count % @bitSizeOf(Limb));
- if (bits_left != 0) {
- const bytes_read = limb_index * @sizeOf(Limb);
- const bytes_left = byte_count - bytes_read;
- var buffer_left = switch (endian) {
- .Little => buffer[bytes_read..],
- .Big => buffer[0..],
- };
+ // Copy the remaining N bytes (N <= @sizeOf(Limb))
+ var bytes_read = limb_index * @sizeOf(Limb);
+ if (bytes_read != byte_count) {
+ var limb: Limb = 0;
- var limb = @intCast(Limb, blk: {
- // zig fmt: off
- if (bytes_left == 1) break :blk mem.readInt( u8, buffer_left[0.. 1], endian);
- if (bytes_left == 2) break :blk mem.readInt( u16, buffer_left[0.. 2], endian);
- if (bytes_left == 4) break :blk mem.readInt( u32, buffer_left[0.. 4], endian);
- if (bytes_left == 8) break :blk mem.readInt( u64, buffer_left[0.. 8], endian);
- if (bytes_left == 16) break :blk mem.readInt(u128, buffer_left[0..16], endian);
- // zig fmt: on
- unreachable;
- });
+ while (bytes_read != byte_count) {
+ const read_size = std.math.floorPowerOfTwo(usize, byte_count - bytes_read);
+ var int_buffer = switch (endian) {
+ .Little => buffer[bytes_read..],
+ .Big => buffer[(abi_size - bytes_read - read_size)..],
+ };
+ limb |= @intCast(Limb, switch (read_size) {
+ 1 => mem.readInt(u8, int_buffer[0..1], endian),
+ 2 => mem.readInt(u16, int_buffer[0..2], endian),
+ 4 => mem.readInt(u32, int_buffer[0..4], endian),
+ 8 => mem.readInt(u64, int_buffer[0..8], endian),
+ 16 => mem.readInt(u128, int_buffer[0..16], endian),
+ else => unreachable,
+ }) << @intCast(Log2Limb, 8 * (bytes_read % @sizeOf(Limb)));
+ bytes_read += read_size;
+ }
// 2's complement (bitwise not, then add carry bit)
if (!positive) _ = @addWithOverflow(Limb, ~limb, carry, &limb);
// Mask off any unused bits
- const mask = (@as(Limb, 1) << bits_left) -% 1; // 0b0..01..1 with (bits_left) trailing ones
+ const valid_bits = @intCast(Log2Limb, bit_count % @bitSizeOf(Limb));
+ const mask = (@as(Limb, 1) << valid_bits) -% 1; // 0b0..01..1 with (valid_bits_in_limb) trailing ones
limb &= mask;
x.limbs[limb_count - 1] = limb;
@@ -2076,21 +2074,16 @@ pub const Const = struct {
}
/// Write the value of `x` into `buffer`
- /// Asserts that `buffer` and `bit_count` are large enough to store the value.
+ /// Asserts that `buffer`, `abi_size`, and `bit_count` are large enough to store the value.
///
- /// For integers with a well-defined layout (e.g. all power-of-two integers), this function
- /// can be thought of as writing to `buffer` the contents of @ptrCast([]const u8, &x),
- /// where the slice length is taken to be @sizeOf(std.meta.Int(_,<bit_count>))
- ///
- /// For integers with a non-well-defined layout, the only requirement is that readTwosComplement
- /// on the same buffer creates an equivalent big integer.
- pub fn writeTwosComplement(x: Const, buffer: []u8, bit_count: usize, endian: Endian) void {
- if (bit_count == 0) return;
+ /// `buffer` is filled so that its contents match what would be observed via
+ /// @ptrCast(*[abi_size]const u8, &x). Byte ordering is determined by `endian`,
+ /// and any required padding bits are added on the MSB end.
+ pub fn writeTwosComplement(x: Const, buffer: []u8, bit_count: usize, abi_size: usize, endian: Endian) void {
- var byte_count = @sizeOf(Limb) * (bit_count / @bitSizeOf(Limb));
- if (bit_count % @bitSizeOf(Limb) != 0) {
- byte_count += (std.math.ceilPowerOfTwoAssert(usize, bit_count % @bitSizeOf(Limb)) + 7) / 8;
- }
+ // byte_count is our total write size
+ const byte_count = abi_size;
+ assert(8 * byte_count >= bit_count);
assert(buffer.len >= byte_count);
assert(x.fitsInTwosComp(if (x.positive) .unsigned else .signed, bit_count));
@@ -2100,7 +2093,7 @@ pub const Const = struct {
while (limb_index < byte_count / @sizeOf(Limb)) : (limb_index += 1) {
var buf_index = switch (endian) {
.Little => @sizeOf(Limb) * limb_index,
- .Big => byte_count - (limb_index + 1) * @sizeOf(Limb),
+ .Big => abi_size - (limb_index + 1) * @sizeOf(Limb),
};
var limb: Limb = if (limb_index < x.limbs.len) x.limbs[limb_index] else 0;
@@ -2111,32 +2104,36 @@ pub const Const = struct {
mem.writeInt(Limb, limb_buf, limb, endian);
}
- // Copy any remaining bytes
- if (byte_count % @sizeOf(Limb) != 0) {
- const bytes_read = limb_index * @sizeOf(Limb);
- const bytes_left = byte_count - bytes_read;
- var buffer_left = switch (endian) {
- .Little => buffer[bytes_read..],
- .Big => buffer[0..],
- };
-
+ // Copy the remaining N bytes (N < @sizeOf(Limb))
+ var bytes_written = limb_index * @sizeOf(Limb);
+ if (bytes_written != byte_count) {
var limb: Limb = if (limb_index < x.limbs.len) x.limbs[limb_index] else 0;
// 2's complement (bitwise not, then add carry bit)
if (!x.positive) _ = @addWithOverflow(Limb, ~limb, carry, &limb);
- if (bytes_left == 1) {
- mem.writeInt(u8, buffer_left[0..1], @truncate(u8, limb), endian);
- } else if (@sizeOf(Limb) > 1 and bytes_left == 2) {
- mem.writeInt(u16, buffer_left[0..2], @truncate(u16, limb), endian);
- } else if (@sizeOf(Limb) > 2 and bytes_left == 4) {
- mem.writeInt(u32, buffer_left[0..4], @truncate(u32, limb), endian);
- } else if (@sizeOf(Limb) > 4 and bytes_left == 8) {
- mem.writeInt(u64, buffer_left[0..8], @truncate(u64, limb), endian);
- } else if (@sizeOf(Limb) > 8 and bytes_left == 16) {
- mem.writeInt(u128, buffer_left[0..16], @truncate(u128, limb), endian);
- } else if (@sizeOf(Limb) > 16) {
- @compileError("@sizeOf(Limb) exceeded supported range");
- } else unreachable;
+ while (bytes_written != byte_count) {
+ const write_size = std.math.floorPowerOfTwo(usize, byte_count - bytes_written);
+ var int_buffer = switch (endian) {
+ .Little => buffer[bytes_written..],
+ .Big => buffer[(abi_size - bytes_written - write_size)..],
+ };
+
+ if (write_size == 1) {
+ mem.writeInt(u8, int_buffer[0..1], @truncate(u8, limb), endian);
+ } else if (@sizeOf(Limb) >= 2 and write_size == 2) {
+ mem.writeInt(u16, int_buffer[0..2], @truncate(u16, limb), endian);
+ } else if (@sizeOf(Limb) >= 4 and write_size == 4) {
+ mem.writeInt(u32, int_buffer[0..4], @truncate(u32, limb), endian);
+ } else if (@sizeOf(Limb) >= 8 and write_size == 8) {
+ mem.writeInt(u64, int_buffer[0..8], @truncate(u64, limb), endian);
+ } else if (@sizeOf(Limb) >= 16 and write_size == 16) {
+ mem.writeInt(u128, int_buffer[0..16], @truncate(u128, limb), endian);
+ } else if (@sizeOf(Limb) >= 32) {
+ @compileError("@sizeOf(Limb) exceeded supported range");
+ } else unreachable;
+ limb >>= @intCast(Log2Limb, 8 * write_size);
+ bytes_written += write_size;
+ }
}
}
lib/std/math/big/int_test.zig
@@ -2498,16 +2498,103 @@ test "big int conversion read/write twos complement" {
defer testing.allocator.free(buffer1);
const endians = [_]std.builtin.Endian{ .Little, .Big };
+ const abi_size = 64;
for (endians) |endian| {
// Writing to buffer and back should not change anything
- a.toConst().writeTwosComplement(buffer1, 493, endian);
- m.readTwosComplement(buffer1, 493, endian, .unsigned);
+ a.toConst().writeTwosComplement(buffer1, 493, abi_size, endian);
+ m.readTwosComplement(buffer1, 493, abi_size, endian, .unsigned);
try testing.expect(m.toConst().order(a.toConst()) == .eq);
// Equivalent to @bitCast(i493, @as(u493, intMax(u493))
- a.toConst().writeTwosComplement(buffer1, 493, endian);
- m.readTwosComplement(buffer1, 493, endian, .signed);
+ a.toConst().writeTwosComplement(buffer1, 493, abi_size, endian);
+ m.readTwosComplement(buffer1, 493, abi_size, endian, .signed);
try testing.expect(m.toConst().orderAgainstScalar(-1) == .eq);
}
}
+
+test "big int conversion read twos complement with padding" {
+ var a = try Managed.initSet(testing.allocator, 0x01_02030405_06070809_0a0b0c0d);
+ defer a.deinit();
+
+ var buffer1 = try testing.allocator.alloc(u8, 16);
+ defer testing.allocator.free(buffer1);
+ @memset(buffer1.ptr, 0xaa, buffer1.len);
+
+ // writeTwosComplement:
+ // (1) should not write beyond buffer[0..abi_size]
+ // (2) should correctly order bytes based on the provided endianness
+ // (3) should sign-extend any bits from bit_count to 8 * abi_size
+
+ var bit_count: usize = 12 * 8 + 1;
+ a.toConst().writeTwosComplement(buffer1, bit_count, 13, .Little);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0xaa, 0xaa, 0xaa }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 13, .Big);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xaa, 0xaa, 0xaa }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 16, .Little);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0x1, 0x0, 0x0, 0x0 }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 16, .Big);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0x0, 0x0, 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd }));
+
+ @memset(buffer1.ptr, 0xaa, buffer1.len);
+ try a.set(-0x01_02030405_06070809_0a0b0c0d);
+ bit_count = 12 * 8 + 2;
+
+ a.toConst().writeTwosComplement(buffer1, bit_count, 13, .Little);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xaa, 0xaa, 0xaa }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 13, .Big);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3, 0xaa, 0xaa, 0xaa }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 16, .Little);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, 0xff, 0xff }));
+ a.toConst().writeTwosComplement(buffer1, bit_count, 16, .Big);
+ try testing.expect(std.mem.eql(u8, buffer1, &[_]u8{ 0xff, 0xff, 0xff, 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3 }));
+}
+
+test "big int conversion write twos complement with padding" {
+ var a = try Managed.initSet(testing.allocator, 0x01_ffffffff_ffffffff_ffffffff);
+ defer a.deinit();
+
+ var m = a.toMutable();
+
+ // readTwosComplement:
+ // (1) should not read beyond buffer[0..abi_size]
+ // (2) should correctly interpret bytes based on the provided endianness
+ // (3) should ignore any bits from bit_count to 8 * abi_size
+
+ var bit_count: usize = 12 * 8 + 1;
+ var buffer: []const u8 = undefined;
+
+ buffer = &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0xb };
+ m.readTwosComplement(buffer, bit_count, 13, .Little, .unsigned);
+ try testing.expect(m.toConst().orderAgainstScalar(0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0xb, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd };
+ m.readTwosComplement(buffer, bit_count, 13, .Big, .unsigned);
+ try testing.expect(m.toConst().orderAgainstScalar(0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 0x2, 0xab, 0xaa, 0xaa, 0xaa };
+ m.readTwosComplement(buffer, bit_count, 16, .Little, .unsigned);
+ try testing.expect(m.toConst().orderAgainstScalar(0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0xaa, 0xaa, 0xaa, 0xab, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd };
+ m.readTwosComplement(buffer, bit_count, 16, .Big, .unsigned);
+ try testing.expect(m.toConst().orderAgainstScalar(0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ bit_count = 12 * 8 + 2;
+
+ buffer = &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0x02 };
+ m.readTwosComplement(buffer, bit_count, 13, .Little, .signed);
+ try testing.expect(m.toConst().orderAgainstScalar(-0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0x02, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3 };
+ m.readTwosComplement(buffer, bit_count, 13, .Big, .signed);
+ try testing.expect(m.toConst().orderAgainstScalar(-0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0xf3, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0x02, 0xaa, 0xaa, 0xaa };
+ m.readTwosComplement(buffer, bit_count, 16, .Little, .signed);
+ try testing.expect(m.toConst().orderAgainstScalar(-0x01_02030405_06070809_0a0b0c0d) == .eq);
+
+ buffer = &[_]u8{ 0xaa, 0xaa, 0xaa, 0x02, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf3 };
+ m.readTwosComplement(buffer, bit_count, 16, .Big, .signed);
+ try testing.expect(m.toConst().orderAgainstScalar(-0x01_02030405_06070809_0a0b0c0d) == .eq);
+}
src/value.zig
@@ -1046,7 +1046,8 @@ pub const Value = extern union {
var bigint_buffer: BigIntSpace = undefined;
const bigint = val.toBigInt(&bigint_buffer);
const bits = ty.intInfo(target).bits;
- bigint.writeTwosComplement(buffer, bits, target.cpu.arch.endian());
+ const abi_size = ty.abiSize(target);
+ bigint.writeTwosComplement(buffer, bits, abi_size, target.cpu.arch.endian());
},
.Enum => {
var enum_buffer: Payload.U64 = undefined;
@@ -1054,7 +1055,8 @@ pub const Value = extern union {
var bigint_buffer: BigIntSpace = undefined;
const bigint = int_val.toBigInt(&bigint_buffer);
const bits = ty.intInfo(target).bits;
- bigint.writeTwosComplement(buffer, bits, target.cpu.arch.endian());
+ const abi_size = ty.abiSize(target);
+ bigint.writeTwosComplement(buffer, bits, abi_size, target.cpu.arch.endian());
},
.Float => switch (ty.floatBits(target)) {
16 => return floatWriteToMemory(f16, val.toFloat(f16), target, buffer),
@@ -1096,8 +1098,9 @@ pub const Value = extern union {
const Limb = std.math.big.Limb;
const limb_count = (buffer.len + @sizeOf(Limb) - 1) / @sizeOf(Limb);
const limbs_buffer = try arena.alloc(Limb, limb_count);
+ const abi_size = ty.abiSize(target);
var bigint = BigIntMutable.init(limbs_buffer, 0);
- bigint.readTwosComplement(buffer, int_info.bits, endian, int_info.signedness);
+ bigint.readTwosComplement(buffer, int_info.bits, abi_size, endian, int_info.signedness);
return fromBigInt(arena, bigint.toConst());
},
.Float => switch (ty.floatBits(target)) {