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fix large f128 values being incorrectly parsed as inf

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Found while fuzzing. Previously 1.1897314953572317650857593266280070162E4932
was parsed as +inf, which caused issues for round-trip serialization of
floats. Only f128 had issues, but have added other tests for all
floating point large normals.

The max_exponent for f128 was wrong, it is subtly different in the
decimal code-path as it is based on where the decimal digit should go.
This needs to be 2 greater than the max exponent (e.g. 308 or 4932) to
work correctly (greater by 1, then we use a >= comparision).

In addition, I've removed the redundant `optimize` constant which was only
use for testing the slow path locally.
This commit is contained in:
Marc Tiehuis
2024-02-25 19:15:22 +13:00
committed by Andrew Kelley
parent 08e886b8fe
commit ff3bf98345
3 changed files with 22 additions and 19 deletions
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32
lib/std/fmt/parse_float/parse_float.zig
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@@ -5,8 +5,6 @@ const convertEiselLemire = @import("convert_eisel_lemire.zig").convertEiselLemir
const convertSlow = @import("convert_slow.zig").convertSlow;
const convertHex = @import("convert_hex.zig").convertHex;
const optimize = true;
pub const ParseFloatError = error{
InvalidCharacter,
};
@@ -41,25 +39,23 @@ pub fn parseFloat(comptime T: type, s: []const u8) ParseFloatError!T {
return convertHex(T, n);
}
if (optimize) {
if (convertFast(T, n)) |f| {
return f;
}
if (convertFast(T, n)) |f| {
return f;
}
if (T == f16 or T == f32 or T == f64) {
// If significant digits were truncated, then we can have rounding error
// only if `mantissa + 1` produces a different result. We also avoid
// redundantly using the Eisel-Lemire algorithm if it was unable to
// correctly round on the first pass.
if (convertEiselLemire(T, n.exponent, n.mantissa)) |bf| {
if (!n.many_digits) {
if (T == f16 or T == f32 or T == f64) {
// If significant digits were truncated, then we can have rounding error
// only if `mantissa + 1` produces a different result. We also avoid
// redundantly using the Eisel-Lemire algorithm if it was unable to
// correctly round on the first pass.
if (convertEiselLemire(T, n.exponent, n.mantissa)) |bf| {
if (!n.many_digits) {
return bf.toFloat(T, n.negative);
}
if (convertEiselLemire(T, n.exponent, n.mantissa + 1)) |bf2| {
if (bf.eql(bf2)) {
return bf.toFloat(T, n.negative);
}
if (convertEiselLemire(T, n.exponent, n.mantissa + 1)) |bf2| {
if (bf.eql(bf2)) {
return bf.toFloat(T, n.negative);
}
}
}
}
}