New submission from STINNER Victor <vstin...@python.org>:
Linux manual page of nextafter():
"""
The nextafter() function return the next representable floating-point value
following x in the direction of y. If y is less than x, these functions will
return the largest representable number less than x.
If x equals y, the functions return y.
"""
I used this function to round an integer towards zero when casting a float to
an integer in bpo-39277. Example in C:
#include <math.h>
#include <stdio.h>
#include <stdint.h>
int main()
{
int64_t int64_max = 9223372036854775807LL;
double d = (double)int64_max; /* ROUND_HALF_EVEN */
double d2 = nextafter(d, 0.0);
printf("i = %ld\n", int64_max);
printf("d = %.0f\n", d);
printf("d2 = %.0f\n", d2);
printf("d - d2 = %.0f\n", d - d2);
return 0;
}
Output:
i = 9223372036854775807
d = 9223372036854775808
d2 = 9223372036854774784
d - d2 = 1024
The function exists in numpy:
numpy.nextafter(x1, x2, /, out=None, *, where=True, casting='same_kind',
order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'nextafter'>
Return the next floating-point value after x1 towards x2, element-wise.
https://docs.scipy.org/doc/numpy/reference/generated/numpy.nextafter.html
Attached PR adds math.nextafter().
----------
components: Library (Lib)
messages: 359731
nosy: vstinner
priority: normal
severity: normal
status: open
title: Add math.nextafter(a, b)
versions: Python 3.9
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39288>
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