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Make overflow arithmetic builtins return tuples #14024

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Dec 27, 2022
Merged

Make overflow arithmetic builtins return tuples #14024

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54160e7
Sema: make overflow arithmetic builtins return tuples
Vexu Dec 21, 2022
622311f
update uses of overflow arithmetic builtins
Vexu Dec 21, 2022
b7730c7
update zig1.wasm to overflow arithmetic builtin changes
Vexu Dec 21, 2022
9c0f316
value: fix bitcasting packed structs with `u0` fields
Vexu Dec 22, 2022
a777373
enable test on more targets
Vexu Dec 21, 2022
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58 changes: 26 additions & 32 deletions doc/langref.html.in
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Original file line number Diff line number Diff line change
Expand Up @@ -5413,14 +5413,14 @@ pub fn parseU64(buf: []const u8, radix: u8) !u64 {
}

// x *= radix
if (@mulWithOverflow(u64, x, radix, &x)) {
return error.Overflow;
}
var ov = @mulWithOverflow(x, radix);
if (ov[1] != 0) return error.OverFlow;


// x += digit
if (@addWithOverflow(u64, x, digit, &x)) {
return error.Overflow;
}
ov = @addWithOverflow(ov[0], digit);
if (ov[1] != 0) return error.OverFlow;
x = ov[0];
}

return x;
Expand Down Expand Up @@ -5832,14 +5832,16 @@ test "merge error sets" {
{#code_begin|test|inferred_error_sets#}
// With an inferred error set
pub fn add_inferred(comptime T: type, a: T, b: T) !T {
var answer: T = undefined;
return if (@addWithOverflow(T, a, b, &answer)) error.Overflow else answer;
const ov = @addWithOverflow(a, b);
if (ov[1] != 0) return error.Overflow;
return ov[0];
}

// With an explicit error set
pub fn add_explicit(comptime T: type, a: T, b: T) Error!T {
var answer: T = undefined;
return if (@addWithOverflow(T, a, b, &answer)) error.Overflow else answer;
const ov = @addWithOverflow(a, b);
if (ov[1] != 0) return error.Overflow;
return ov[0];
}

const Error = error {
Expand Down Expand Up @@ -7632,11 +7634,9 @@ test "global assembly" {
</p>
{#header_close#}
{#header_open|@addWithOverflow#}
<pre>{#syntax#}@addWithOverflow(comptime T: type, a: T, b: T, result: *T) bool{#endsyntax#}</pre>
<pre>{#syntax#}@addWithOverflow(a: anytype, b: anytype) struct { @TypeOf(a, b), u1 }{#endsyntax#}</pre>
<p>
Performs {#syntax#}result.* = a + b{#endsyntax#}. If overflow or underflow occurs,
stores the overflowed bits in {#syntax#}result{#endsyntax#} and returns {#syntax#}true{#endsyntax#}.
If no overflow or underflow occurs, returns {#syntax#}false{#endsyntax#}.
Performs {#syntax#}a + b{#endsyntax#} and returns a tuple with the result and a possible overflow bit.
</p>
{#header_close#}
{#header_open|@alignCast#}
Expand Down Expand Up @@ -8695,11 +8695,9 @@ test "@wasmMemoryGrow" {
{#header_close#}

{#header_open|@mulWithOverflow#}
<pre>{#syntax#}@mulWithOverflow(comptime T: type, a: T, b: T, result: *T) bool{#endsyntax#}</pre>
<pre>{#syntax#}@mulWithOverflow(a: anytype, b: anytype) struct { @TypeOf(a, b), u1 }{#endsyntax#}</pre>
<p>
Performs {#syntax#}result.* = a * b{#endsyntax#}. If overflow or underflow occurs,
stores the overflowed bits in {#syntax#}result{#endsyntax#} and returns {#syntax#}true{#endsyntax#}.
If no overflow or underflow occurs, returns {#syntax#}false{#endsyntax#}.
Performs {#syntax#}a * b{#endsyntax#} and returns a tuple with the result and a possible overflow bit.
</p>
{#header_close#}

Expand Down Expand Up @@ -8973,15 +8971,13 @@ test "@setRuntimeSafety" {
{#header_close#}

{#header_open|@shlWithOverflow#}
<pre>{#syntax#}@shlWithOverflow(comptime T: type, a: T, shift_amt: Log2T, result: *T) bool{#endsyntax#}</pre>
<pre>{#syntax#}@shlWithOverflow(a: anytype, shift_amt: Log2T) struct { @TypeOf(a), u1 }{#endsyntax#}</pre>
<p>
Performs {#syntax#}result.* = a << b{#endsyntax#}. If overflow or underflow occurs,
stores the overflowed bits in {#syntax#}result{#endsyntax#} and returns {#syntax#}true{#endsyntax#}.
If no overflow or underflow occurs, returns {#syntax#}false{#endsyntax#}.
Performs {#syntax#}a << b{#endsyntax#} and returns a tuple with the result and a possible overflow bit.
</p>
<p>
The type of {#syntax#}shift_amt{#endsyntax#} is an unsigned integer with {#syntax#}log2(@typeInfo(T).Int.bits){#endsyntax#} bits.
This is because {#syntax#}shift_amt >= @typeInfo(T).Int.bits{#endsyntax#} is undefined behavior.
The type of {#syntax#}shift_amt{#endsyntax#} is an unsigned integer with {#syntax#}log2(@typeInfo(@TypeOf(a)).Int.bits){#endsyntax#} bits.
This is because {#syntax#}shift_amt >= @typeInfo(@TypeOf(a)).Int.bits{#endsyntax#} is undefined behavior.
</p>
{#see_also|@shlExact|@shrExact#}
{#header_close#}
Expand Down Expand Up @@ -9323,11 +9319,9 @@ fn doTheTest() !void {
{#header_close#}

{#header_open|@subWithOverflow#}
<pre>{#syntax#}@subWithOverflow(comptime T: type, a: T, b: T, result: *T) bool{#endsyntax#}</pre>
<pre>{#syntax#}@subWithOverflow(a: anytype, b: anytype) struct { @TypeOf(a, b), u1 }{#endsyntax#}</pre>
<p>
Performs {#syntax#}result.* = a - b{#endsyntax#}. If overflow or underflow occurs,
stores the overflowed bits in {#syntax#}result{#endsyntax#} and returns {#syntax#}true{#endsyntax#}.
If no overflow or underflow occurs, returns {#syntax#}false{#endsyntax#}.
Performs {#syntax#}a - b{#endsyntax#} and returns a tuple with the result and a possible overflow bit.
</p>
{#header_close#}

Expand Down Expand Up @@ -9774,11 +9768,11 @@ const print = @import("std").debug.print;
pub fn main() void {
var byte: u8 = 255;

var result: u8 = undefined;
if (@addWithOverflow(u8, byte, 10, &result)) {
print("overflowed result: {}\n", .{result});
const ov = @addWithOverflow(byte, 10);
if (ov[1] != 0) {
print("overflowed result: {}\n", .{ov[0]});
} else {
print("result: {}\n", .{result});
print("result: {}\n", .{ov[0]});
}
}
{#code_end#}
Expand Down
14 changes: 8 additions & 6 deletions lib/compiler_rt/trunctfxf2.zig
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Expand Up @@ -49,14 +49,16 @@ pub fn __trunctfxf2(a: f128) callconv(.C) f80 {
const round_bits = a_abs & round_mask;
if (round_bits > halfway) {
// Round to nearest
const carry = @boolToInt(@addWithOverflow(u64, res.fraction, 1, &res.fraction));
res.exp += carry;
res.fraction |= @as(u64, carry) << 63; // Restore integer bit after carry
const ov = @addWithOverflow(res.fraction, 1);
res.fraction = ov[0];
res.exp += ov[1];
res.fraction |= @as(u64, ov[1]) << 63; // Restore integer bit after carry
Comment on lines +52 to +55
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Ignore this if this was already discussed and firmly agreed on as-is internally but like I said in my comment in the issue (#10248 (comment)), a regular struct with named fields would be much easier to read here (e.g. struct { result: T, overflow: u1 }). Now I'm going to have to memorize what the result value is and what the overflow value is.

These are now the first builtins to my knowledge with this kind of rather not so obvious return type.

If Zig gets destructuring assignment in the future, the situation might improve a bit, though.

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Just found that functions like std.math.add, std.math.mul, etc are doing exactly this using builtins as the lower-level construct under the hood. So, for safe math one should just use standard lib functions I guess.

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Those std.math variants do look like they can be a more readable alternative.

} else if (round_bits == halfway) {
// Ties to even
const carry = @boolToInt(@addWithOverflow(u64, res.fraction, res.fraction & 1, &res.fraction));
res.exp += carry;
res.fraction |= @as(u64, carry) << 63; // Restore integer bit after carry
const ov = @addWithOverflow(res.fraction, res.fraction & 1);
res.fraction = ov[0];
res.exp += ov[1];
res.fraction |= @as(u64, ov[1]) << 63; // Restore integer bit after carry
}
if (res.exp == 0) res.fraction &= ~@as(u64, integer_bit); // Remove integer bit for de-normals
}
Expand Down
4 changes: 1 addition & 3 deletions lib/std/compress/deflate/compressor_test.zig
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Expand Up @@ -172,9 +172,7 @@ test "deflate/inflate" {
defer testing.allocator.free(large_data_chunk);
// fill with random data
for (large_data_chunk) |_, i| {
var mul: u8 = @truncate(u8, i);
_ = @mulWithOverflow(u8, mul, mul, &mul);
large_data_chunk[i] = mul;
large_data_chunk[i] = @truncate(u8, i) *% @truncate(u8, i);
}
try testToFromWithLimit(large_data_chunk, limits);
}
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/p256/p256_64.zig
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Expand Up @@ -75,10 +75,10 @@ pub const NonMontgomeryDomainFieldElement = [4]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -97,10 +97,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/p256/p256_scalar_64.zig
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Expand Up @@ -75,10 +75,10 @@ pub const NonMontgomeryDomainFieldElement = [4]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -97,10 +97,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/p384/p384_64.zig
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Expand Up @@ -44,10 +44,10 @@ pub const NonMontgomeryDomainFieldElement = [6]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -66,10 +66,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/p384/p384_scalar_64.zig
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Expand Up @@ -44,10 +44,10 @@ pub const NonMontgomeryDomainFieldElement = [6]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -66,10 +66,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/secp256k1/secp256k1_64.zig
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Expand Up @@ -44,10 +44,10 @@ pub const NonMontgomeryDomainFieldElement = [4]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -66,10 +66,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
16 changes: 8 additions & 8 deletions lib/std/crypto/pcurves/secp256k1/secp256k1_scalar_64.zig
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Expand Up @@ -44,10 +44,10 @@ pub const NonMontgomeryDomainFieldElement = [4]u64;
inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @addWithOverflow(u64, arg2, arg3, &t);
const carry2 = @addWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @addWithOverflow(arg2, arg3);
const ov2 = @addWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function subborrowxU64 is a subtraction with borrow.
Expand All @@ -66,10 +66,10 @@ inline fn addcarryxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) vo
inline fn subborrowxU64(out1: *u64, out2: *u1, arg1: u1, arg2: u64, arg3: u64) void {
@setRuntimeSafety(mode == .Debug);

var t: u64 = undefined;
const carry1 = @subWithOverflow(u64, arg2, arg3, &t);
const carry2 = @subWithOverflow(u64, t, arg1, out1);
out2.* = @boolToInt(carry1) | @boolToInt(carry2);
const ov1 = @subWithOverflow(arg2, arg3);
const ov2 = @subWithOverflow(ov1[0], arg1);
out1.* = ov2[0];
out2.* = ov1[1] | ov2[1];
}

/// The function mulxU64 is a multiplication, returning the full double-width result.
Expand Down
4 changes: 3 additions & 1 deletion lib/std/crypto/salsa20.zig
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Expand Up @@ -263,7 +263,9 @@ fn SalsaNonVecImpl(comptime rounds: comptime_int) type {
while (j < 64) : (j += 1) {
xout[j] ^= buf[j];
}
ctx[9] += @boolToInt(@addWithOverflow(u32, ctx[8], 1, &ctx[8]));
const ov = @addWithOverflow(ctx[8], 1);
ctx[8] = ov[0];
ctx[9] += ov[1];
}
if (i < in.len) {
salsaCore(x[0..], ctx, true);
Expand Down
24 changes: 16 additions & 8 deletions lib/std/crypto/utils.zig
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Expand Up @@ -87,15 +87,19 @@ pub fn timingSafeAdd(comptime T: type, a: []const T, b: []const T, result: []T,
if (endian == .Little) {
var i: usize = 0;
while (i < len) : (i += 1) {
const tmp = @boolToInt(@addWithOverflow(u8, a[i], b[i], &result[i]));
carry = tmp | @boolToInt(@addWithOverflow(u8, result[i], carry, &result[i]));
const ov1 = @addWithOverflow(a[i], b[i]);
const ov2 = @addWithOverflow(ov1[0], carry);
result[i] = ov2[0];
carry = ov1[1] | ov2[1];
}
} else {
var i: usize = len;
while (i != 0) {
i -= 1;
const tmp = @boolToInt(@addWithOverflow(u8, a[i], b[i], &result[i]));
carry = tmp | @boolToInt(@addWithOverflow(u8, result[i], carry, &result[i]));
const ov1 = @addWithOverflow(a[i], b[i]);
const ov2 = @addWithOverflow(ov1[0], carry);
result[i] = ov2[0];
carry = ov1[1] | ov2[1];
}
}
return @bitCast(bool, carry);
Expand All @@ -110,15 +114,19 @@ pub fn timingSafeSub(comptime T: type, a: []const T, b: []const T, result: []T,
if (endian == .Little) {
var i: usize = 0;
while (i < len) : (i += 1) {
const tmp = @boolToInt(@subWithOverflow(u8, a[i], b[i], &result[i]));
borrow = tmp | @boolToInt(@subWithOverflow(u8, result[i], borrow, &result[i]));
const ov1 = @subWithOverflow(a[i], b[i]);
const ov2 = @subWithOverflow(ov1[0], borrow);
result[i] = ov2[0];
borrow = ov1[1] | ov2[1];
}
} else {
var i: usize = len;
while (i != 0) {
i -= 1;
const tmp = @boolToInt(@subWithOverflow(u8, a[i], b[i], &result[i]));
borrow = tmp | @boolToInt(@subWithOverflow(u8, result[i], borrow, &result[i]));
const ov1 = @subWithOverflow(a[i], b[i]);
const ov2 = @subWithOverflow(ov1[0], borrow);
result[i] = ov2[0];
borrow = ov1[1] | ov2[1];
}
}
return @bitCast(bool, borrow);
Expand Down
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