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std.math.big.int: fix format functions

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Justus Klausecker 2025-11-14 10:34:23 +01:00 • committed by Andrew Kelley
parent 16fc083f2b
commit e5c2df9f17
1 changed files with 35 additions and 1 deletions
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36
lib/std/math/big/int.zig
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@ -2032,7 +2032,11 @@ pub const Mutable = struct {
return formatNumber(self, w, .{});
}
pub fn formatNumber(self: Const, w: *std.Io.Writer, n: std.fmt.Number) std.Io.Writer.Error!void {
/// 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 `Const.toString` and `Const.toStringAlloc` for a way to print big integers without failure.
pub fn formatNumber(self: Mutable, w: *std.Io.Writer, n: std.fmt.Number) std.Io.Writer.Error!void {
return self.toConst().formatNumber(w, n);
}
};
@ -2321,6 +2325,10 @@ pub const Const = struct {
return .{ normalized_res.reconstruct(if (self.positive) .positive else .negative), exactness };
}
pub fn format(self: Const, w: *std.Io.Writer) std.Io.Writer.Error!void {
return self.formatNumber(w, .{});
}
/// 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.
@ -4625,3 +4633,29 @@ fn testOneShiftCaseAliasing(func: fn ([]Limb, []const Limb, usize) usize, case:
try std.testing.expectEqualSlices(Limb, expected, r[base .. base + len]);
}
}
test "format" {
var a: Managed = try .init(std.testing.allocator);
defer a.deinit();
try a.set(123);
try testFormat(a, "123");
try a.set(-123);
try testFormat(a, "-123");
try a.set(20000000000000000000); // > maxInt(u64)
try testFormat(a, "20000000000000000000");
try a.set(1 << 64 * @sizeOf(usize) * 8);
try testFormat(a, "(BigInt)");
try a.set(-(1 << 64 * @sizeOf(usize) * 8));
try testFormat(a, "(BigInt)");
}
fn testFormat(a: Managed, expected: []const u8) !void {
try std.testing.expectFmt(expected, "{f}", .{a});
try std.testing.expectFmt(expected, "{f}", .{a.toMutable()});
try std.testing.expectFmt(expected, "{f}", .{a.toConst()});
}