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Merge pull request #8330 from kivikakk/single-limb-bigint-overflow

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bigint add failures with aliasing
This commit is contained in:
Veikka Tuominen 2021-06-11 19:17:01 +03:00 committed by GitHub
commit 0bde5ce369
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2 changed files with 60 additions and 7 deletions
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28
lib/std/math/big/int.zig
View File

@ -316,7 +316,9 @@ pub const Mutable = struct {
}
if (a.limbs.len == 1 and b.limbs.len == 1 and a.positive == b.positive) {
if (!@addWithOverflow(Limb, a.limbs[0], b.limbs[0], &r.limbs[0])) {
var o: Limb = undefined;
if (!@addWithOverflow(Limb, a.limbs[0], b.limbs[0], &o)) {
r.limbs[0] = o;
r.len = 1;
r.positive = a.positive;
return;
@ -333,10 +335,10 @@ pub const Mutable = struct {
}
} else {
if (a.limbs.len >= b.limbs.len) {
lladd(r.limbs[0..], a.limbs[0..a.limbs.len], b.limbs[0..b.limbs.len]);
lladd(r.limbs[0..], a.limbs, b.limbs);
r.normalize(a.limbs.len + 1);
} else {
lladd(r.limbs[0..], b.limbs[0..b.limbs.len], a.limbs[0..a.limbs.len]);
lladd(r.limbs[0..], b.limbs, a.limbs);
r.normalize(b.limbs.len + 1);
}
@ -1683,12 +1685,14 @@ pub const Managed = struct {
/// r = a + scalar
///
/// r and a may be aliases.
/// r and a may be aliases. If r aliases a, then caller must call
/// `r.ensureAddScalarCapacity` prior to calling `add`.
/// scalar is a primitive integer type.
///
/// Returns an error if memory could not be allocated.
pub fn addScalar(r: *Managed, a: Const, scalar: anytype) Allocator.Error!void {
try r.ensureCapacity(math.max(a.limbs.len, calcLimbLen(scalar)) + 1);
assert((r.limbs.ptr != a.limbs.ptr) or r.limbs.len >= math.max(a.limbs.len, calcLimbLen(scalar)) + 1);
try r.ensureAddScalarCapacity(a, scalar);
var m = r.toMutable();
m.addScalar(a, scalar);
r.setMetadata(m.positive, m.len);
@ -1696,11 +1700,13 @@ pub const Managed = struct {
/// r = a + b
///
/// r, a and b may be aliases.
/// r, a and b may be aliases. If r aliases a or b, then caller must call
/// `r.ensureAddCapacity` prior to calling `add`.
///
/// Returns an error if memory could not be allocated.
pub fn add(r: *Managed, a: Const, b: Const) Allocator.Error!void {
try r.ensureCapacity(math.max(a.limbs.len, b.limbs.len) + 1);
assert((r.limbs.ptr != a.limbs.ptr and r.limbs.ptr != b.limbs.ptr) or r.limbs.len >= math.max(a.limbs.len, b.limbs.len) + 1);
try r.ensureAddCapacity(a, b);
var m = r.toMutable();
m.add(a, b);
r.setMetadata(m.positive, m.len);
@ -1746,6 +1752,14 @@ pub const Managed = struct {
rma.setMetadata(m.positive, m.len);
}
pub fn ensureAddScalarCapacity(r: *Managed, a: Const, scalar: anytype) !void {
try r.ensureCapacity(math.max(a.limbs.len, calcLimbLen(scalar)) + 1);
}
pub fn ensureAddCapacity(r: *Managed, a: Const, b: Const) !void {
try r.ensureCapacity(math.max(a.limbs.len, b.limbs.len) + 1);
}
pub fn ensureMulCapacity(rma: *Managed, a: Const, b: Const) !void {
try rma.ensureCapacity(a.limbs.len + b.limbs.len + 1);
}

39
lib/std/math/big/int_test.zig
View File

@ -538,6 +538,17 @@ test "big.int add sign" {
try testing.expect((try a.to(i32)) == -3);
}
test "big.int add scalar" {
var a = try Managed.initSet(testing.allocator, 50);
defer a.deinit();
var b = try Managed.init(testing.allocator);
defer b.deinit();
try b.addScalar(a.toConst(), 5);
try testing.expect((try b.to(u32)) == 55);
}
test "big.int sub single-single" {
var a = try Managed.initSet(testing.allocator, 50);
defer a.deinit();
@ -1562,3 +1573,31 @@ test "big.int pow" {
try testing.expectEqual(@as(i32, 1), try a.to(i32));
}
}
test "big.int regression test for 1 limb overflow with alias" {
// Note these happen to be two consecutive Fibonacci sequence numbers, the
// first two whose sum exceeds 2**64.
var a = try Managed.initSet(testing.allocator, 7540113804746346429);
defer a.deinit();
var b = try Managed.initSet(testing.allocator, 12200160415121876738);
defer b.deinit();
try a.ensureAddCapacity(a.toConst(), b.toConst());
try a.add(a.toConst(), b.toConst());
try testing.expect(a.toConst().orderAgainstScalar(19740274219868223167) == .eq);
}
test "big.int regression test for realloc with alias" {
// Note these happen to be two consecutive Fibonacci sequence numbers, the
// second of which is the first such number to exceed 2**192.
var a = try Managed.initSet(testing.allocator, 5611500259351924431073312796924978741056961814867751431689);
defer a.deinit();
var b = try Managed.initSet(testing.allocator, 9079598147510263717870894449029933369491131786514446266146);
defer b.deinit();
try a.ensureAddCapacity(a.toConst(), b.toConst());
try a.add(a.toConst(), b.toConst());
try testing.expect(a.toConst().orderAgainstScalar(14691098406862188148944207245954912110548093601382197697835) == .eq);
}