Note that some ES implementation uses NaN-based tagging to distinguish Number values from internal object pointers. Allowing generation of arbitrary bit pattern FP values would open the door for pointer spoofing. At the very least, implementation would have to reject any such hex fp literals that the implementation would interpret as a pointer.
Allen On Mar 18, 2012, at 6:27 PM, Roger Andrews wrote: > As a C-like language JavaScript has hexadecimal integer literals like > 0x123ABC. > > C99 introduced hexadecimal floating-point literals, see: > http://publib.boulder.ibm.com/infocenter/zos/v1r12/topic/com.ibm.zos.r12.cbclx01/lit_fltpt.htm#lit_fltpt__hex_float_constants > > of the general form: > [sign] "0x" [hexdigits] ["." hexdigits] ["p" [sign] decdigits] > (with the proviso that at least one significant hexdigit must appear). > > The letter 'p' means "times 2 to the power of"; and the exponent field is > signed decimal. Case is ignored. > > (In C the exponent field *must* appear in order to disambiguate a trailing > 'f' = float flag, but this would not be necessary in JavaScript.) > > > Would it be a Big Ask to have hexadecimal floating-point literals in ES6? > It extends the existing hexadecimal integer literal syntax slightly to > encompass all the finite Numbers. > > This gives the programmer the ability to precisely specify every bit of a > Number in a well-understood form. And it is a natural match with the > binary64 sign-significand-exponent fields. > For example: > var EPSILON = 1p-52, > MAX_POWTWO = 1p1023; > instead of > var EPSILON = 1 / 0x10000000000000, > MAX_POWTWO = 1 / (Number.MIN_VALUE * 0x8000000000000); > > JavaScript Numbers can be integer or fractional, decimal literals too, why do > hexadecimal literals discriminate against fractions? > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
