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std.math.big.int.Managed: adjust size of arg for limbs_buffer in format()

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poypoyan 2024-05-21 21:28:05 +08:00 committed by GitHub
parent 33d7815813
commit aa07366513
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2 changed files with 56 additions and 9 deletions
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16
lib/std/math/big/int.zig
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@ -2201,8 +2201,8 @@ pub const Const = struct {
}
/// To allow `std.fmt.format` to work with this type.
/// If the integer is larger than `pow(2, 64 * @sizeOf(usize) * 8), this function will fail
/// to print the string, printing "(BigInt)" instead of a number.
/// If the absolute value of integer is greater than or equal to `pow(2, 64 * @sizeOf(usize) * 8)`,
/// this function will fail to print the string, printing "(BigInt)" instead of a number.
/// This is because the rendering algorithm requires reversing a string, which requires O(N) memory.
/// See `toString` and `toStringAlloc` for a way to print big integers without failure.
pub fn format(
@ -2231,13 +2231,11 @@ pub const Const = struct {
std.fmt.invalidFmtError(fmt, self);
}
var limbs: [128]Limb = undefined;
const needed_limbs = calcDivLimbsBufferLen(self.limbs.len, 1);
if (needed_limbs > limbs.len)
const available_len = 64;
if (self.limbs.len > available_len)
return out_stream.writeAll("(BigInt)");
// This is the inverse of calcDivLimbsBufferLen
const available_len = (limbs.len / 3) - 2;
var limbs: [calcToStringLimbsBufferLen(available_len, base)]Limb = undefined;
const biggest: Const = .{
.limbs = &([1]Limb{comptime math.maxInt(Limb)} ** available_len),
@ -2804,8 +2802,8 @@ pub const Managed = struct {
}
/// To allow `std.fmt.format` to work with `Managed`.
/// If the integer is larger than `pow(2, 64 * @sizeOf(usize) * 8), this function will fail
/// to print the string, printing "(BigInt)" instead of a number.
/// If the absolute value of integer is greater than or equal to `pow(2, 64 * @sizeOf(usize) * 8)`,
/// this function will fail to print the string, printing "(BigInt)" instead of a number.
/// This is because the rendering algorithm requires reversing a string, which requires O(N) memory.
/// See `toString` and `toStringAlloc` for a way to print big integers without failure.
pub fn format(

49
lib/std/math/big/int_test.zig
View File

@ -3232,3 +3232,52 @@ test "Managed sqrt(n) succeed with res.bitCountAbs() >= usize bits" {
try expected.setString(10, "11663466984815033033");
try std.testing.expectEqual(std.math.Order.eq, expected.order(res));
}
test "(BigInt) positive" {
var a = try Managed.initSet(testing.allocator, 2);
defer a.deinit();
var b = try Managed.init(testing.allocator);
defer b.deinit();
var c = try Managed.initSet(testing.allocator, 1);
defer c.deinit();
// a = pow(2, 64 * @sizeOf(usize) * 8), b = a - 1
try a.pow(&a, 64 * @sizeOf(Limb) * 8);
try b.sub(&a, &c);
const a_fmt = try std.fmt.allocPrintZ(testing.allocator, "{d}", .{a});
defer testing.allocator.free(a_fmt);
const b_fmt = try std.fmt.allocPrintZ(testing.allocator, "{d}", .{b});
defer testing.allocator.free(b_fmt);
try testing.expect(mem.eql(u8, a_fmt, "(BigInt)"));
try testing.expect(!mem.eql(u8, b_fmt, "(BigInt)"));
}
test "(BigInt) negative" {
var a = try Managed.initSet(testing.allocator, 2);
defer a.deinit();
var b = try Managed.init(testing.allocator);
defer b.deinit();
var c = try Managed.initSet(testing.allocator, 1);
defer c.deinit();
// a = -pow(2, 64 * @sizeOf(usize) * 8), b = a + 1
try a.pow(&a, 64 * @sizeOf(Limb) * 8);
a.negate();
try b.add(&a, &c);
const a_fmt = try std.fmt.allocPrintZ(testing.allocator, "{d}", .{a});
defer testing.allocator.free(a_fmt);
const b_fmt = try std.fmt.allocPrintZ(testing.allocator, "{d}", .{b});
defer testing.allocator.free(b_fmt);
try testing.expect(mem.eql(u8, a_fmt, "(BigInt)"));
try testing.expect(!mem.eql(u8, b_fmt, "(BigInt)"));
}