0007690: issues with caml_float_of_hex

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0007690

OCaml

standard library

public

2017-12-13 15:46

2017-12-19 15:24

Reporter

oandrieu

Assigned To

nojebar

Priority

normal

Severity

minor

Reproducibility

always

Status

resolved

Resolution

fixed

Platform

OS Version

Product Version

4.03.0

Target Version

Fixed in Version

Summary

0007690: issues with caml_float_of_hex

Description

There are some overflow issues with the exponent computations in caml_float_of_hex, which results in some invalid conversions. The integer exp variable overflows, which results in the call to ldexp to overflow when it should underflow (and vice versa).

The test "if (e < INT_MIN || e > INT_MAX) return -1;" is ineffective on Win64 since int and long have the same size there: this results in some difference in behavior between win64 and linux.

And (minor point), the function accept spaces between the 'p' and the exponent digits, whereas strtod and the C99 syntax do not allow spaces there.

Steps To Reproduce

$ cat f.ml
let hexstring_of_float x =
  Printf.sprintf "%h" x

let () =
  let s =
    try hexstring_of_float (float_of_string Sys.argv.(1))
    with _ -> "invalid" in
  print_endline s

$ ocamlopt.opt f.ml

$ ./a.out 0x1.0p-2147483648
infinity

$ ./a.out 0x123456789ABCDEF0p2147483647
0x0p+0

$ ./a.out 0x1p2147483648
-> invalid on linux64
-> infinity on win64

$ ./a.out '0x1p 1'
0x1p+1

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Notes
(0018743) oandrieu (reporter) 2017-12-13 17:12	I can provide a GPR if you think these corner cases are worth fixing.

(0018744) nojebar (developer) 2017-12-13 17:14	Definitely the overflow one needs fixing; a GPR would be much appreciated! Regarding the second one, I am not sure if it is a bug or not at the moment.

(0018745) oandrieu (reporter) 2017-12-13 20:09	there, GPR#1528 : https://github.com/ocaml/ocaml/pull/1528 [^]

(0018752) nojebar (developer) 2017-12-19 15:24	This PR has now been merged, so marking this resolved.

Issue History
Date Modified	Username	Field	Change
2017-12-13 15:46	oandrieu	New Issue
2017-12-13 17:12	oandrieu	Note Added: 0018743
2017-12-13 17:14	nojebar	Note Added: 0018744
2017-12-13 20:09	oandrieu	Note Added: 0018745
2017-12-19 15:24	nojebar	Note Added: 0018752
2017-12-19 15:24	nojebar	Status	new => resolved
2017-12-19 15:24	nojebar	Resolution	open => fixed
2017-12-19 15:24	nojebar	Assigned To	=> nojebar