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bpo-45995: add "z" format specifer to coerce negative 0 to zero (GH-30049)

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Add "z" format specifier to coerce negative 0 to zero.

See https://github.com/python/cpython/issues/90153 (originally https://bugs.python.org/issue45995) for discussion.
This covers `str.format()` and f-strings.  Old-style string interpolation is not supported.

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>
This commit is contained in:
John Belmonte 2022-04-11 23:34:18 +09:00 • committed by GitHub
parent dd207a6ac5
commit b0b836b20c
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GPG key ID: 4AEE18F83AFDEB23
16 changed files with 368 additions and 43 deletions
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126
Modules/_decimal/_decimal.c
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@ -3183,6 +3183,56 @@ dotsep_as_utf8(const char *s)
return utf8;
}
/* copy of libmpdec _mpd_round() */
static void
_mpd_round(mpd_t *result, const mpd_t *a, mpd_ssize_t prec,
const mpd_context_t *ctx, uint32_t *status)
{
mpd_ssize_t exp = a->exp + a->digits - prec;
if (prec <= 0) {
mpd_seterror(result, MPD_Invalid_operation, status);
return;
}
if (mpd_isspecial(a) || mpd_iszero(a)) {
mpd_qcopy(result, a, status);
return;
}
mpd_qrescale_fmt(result, a, exp, ctx, status);
if (result->digits > prec) {
mpd_qrescale_fmt(result, result, exp+1, ctx, status);
}
}
/* Locate negative zero "z" option within a UTF-8 format spec string.
* Returns pointer to "z", else NULL.
* The portion of the spec we're working with is [[fill]align][sign][z] */
static const char *
format_spec_z_search(char const *fmt, Py_ssize_t size) {
char const *pos = fmt;
char const *fmt_end = fmt + size;
/* skip over [[fill]align] (fill may be multi-byte character) */
pos += 1;
while (pos < fmt_end && *pos & 0x80) {
pos += 1;
}
if (pos < fmt_end && strchr("<>=^", *pos) != NULL) {
pos += 1;
} else {
/* fill not present-- skip over [align] */
pos = fmt;
if (pos < fmt_end && strchr("<>=^", *pos) != NULL) {
pos += 1;
}
}
/* skip over [sign] */
if (pos < fmt_end && strchr("+- ", *pos) != NULL) {
pos += 1;
}
return pos < fmt_end && *pos == 'z' ? pos : NULL;
}
static int
dict_get_item_string(PyObject *dict, const char *key, PyObject **valueobj, const char **valuestr)
{
@ -3220,11 +3270,16 @@ dec_format(PyObject *dec, PyObject *args)
PyObject *fmtarg;
PyObject *context;
mpd_spec_t spec;
char *fmt;
char const *fmt;
char *fmt_copy = NULL;
char *decstring = NULL;
uint32_t status = 0;
int replace_fillchar = 0;
int no_neg_0 = 0;
Py_ssize_t size;
mpd_t *mpd = MPD(dec);
mpd_uint_t dt[MPD_MINALLOC_MAX];
mpd_t tmp = {MPD_STATIC|MPD_STATIC_DATA,0,0,0,MPD_MINALLOC_MAX,dt};
CURRENT_CONTEXT(context);
@ -3233,19 +3288,39 @@ dec_format(PyObject *dec, PyObject *args)
}
if (PyUnicode_Check(fmtarg)) {
fmt = (char *)PyUnicode_AsUTF8AndSize(fmtarg, &size);
fmt = PyUnicode_AsUTF8AndSize(fmtarg, &size);
if (fmt == NULL) {
return NULL;
}
/* NOTE: If https://github.com/python/cpython/pull/29438 lands, the
* format string manipulation below can be eliminated by enhancing
* the forked mpd_parse_fmt_str(). */
if (size > 0 && fmt[0] == '\0') {
/* NUL fill character: must be replaced with a valid UTF-8 char
before calling mpd_parse_fmt_str(). */
replace_fillchar = 1;
fmt = dec_strdup(fmt, size);
if (fmt == NULL) {
fmt = fmt_copy = dec_strdup(fmt, size);
if (fmt_copy == NULL) {
return NULL;
}
fmt[0] = '_';
fmt_copy[0] = '_';
}
/* Strip 'z' option, which isn't understood by mpd_parse_fmt_str().
* NOTE: fmt is always null terminated by PyUnicode_AsUTF8AndSize() */
char const *z_position = format_spec_z_search(fmt, size);
if (z_position != NULL) {
no_neg_0 = 1;
size_t z_index = z_position - fmt;
if (fmt_copy == NULL) {
fmt = fmt_copy = dec_strdup(fmt, size);
if (fmt_copy == NULL) {
return NULL;
}
}
/* Shift characters (including null terminator) left,
overwriting the 'z' option. */
memmove(fmt_copy + z_index, fmt_copy + z_index + 1, size - z_index);
size -= 1;
}
}
else {
@ -3311,8 +3386,45 @@ dec_format(PyObject *dec, PyObject *args)
}
}
if (no_neg_0 && mpd_isnegative(mpd) && !mpd_isspecial(mpd)) {
/* Round into a temporary (carefully mirroring the rounding
of mpd_qformat_spec()), and check if the result is negative zero.
If so, clear the sign and format the resulting positive zero. */
mpd_ssize_t prec;
mpd_qcopy(&tmp, mpd, &status);
if (spec.prec >= 0) {
switch (spec.type) {
case 'f':
mpd_qrescale(&tmp, &tmp, -spec.prec, CTX(context), &status);
break;
case '%':
tmp.exp += 2;
mpd_qrescale(&tmp, &tmp, -spec.prec, CTX(context), &status);
break;
case 'g':
prec = (spec.prec == 0) ? 1 : spec.prec;
if (tmp.digits > prec) {
_mpd_round(&tmp, &tmp, prec, CTX(context), &status);
}
break;
case 'e':
if (!mpd_iszero(&tmp)) {
_mpd_round(&tmp, &tmp, spec.prec+1, CTX(context), &status);
}
break;
}
}
if (status & MPD_Errors) {
PyErr_SetString(PyExc_ValueError, "unexpected error when rounding");
goto finish;
}
if (mpd_iszero(&tmp)) {
mpd_set_positive(&tmp);
mpd = &tmp;
}
}
decstring = mpd_qformat_spec(MPD(dec), &spec, CTX(context), &status);
decstring = mpd_qformat_spec(mpd, &spec, CTX(context), &status);
if (decstring == NULL) {
if (status & MPD_Malloc_error) {
PyErr_NoMemory();
@ -3335,7 +3447,7 @@ finish:
Py_XDECREF(grouping);
Py_XDECREF(sep);
Py_XDECREF(dot);
if (replace_fillchar) PyMem_Free(fmt);
if (fmt_copy) PyMem_Free(fmt_copy);
if (decstring) mpd_free(decstring);
return result;
}