In GNU Emacs 31.0.50 (build 1, x86_64-w64-mingw32) of 2025-01-10 built on AMIRALIRAJA2ACF
Repository revision: 42a5ac3b513ff03c64c9609fc7e79c2b7932b2a4
Repository branch: master
System Description: M1 Mac Book Pro running Windows 11 VM using Parallels

Configured using:
'configure --enable-checking --prefix=/c/emacs --without-dbus
'CFLAGS=-ggdb3 -O0' LDFLAGS=-ggdb3'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

Important settings:
value of $LC_CTYPE: en_US.UTF-8
value of $LANG: ENU
locale-coding-system: cp1252

Minimum repro:
emacs -Q
M-x customize-mode
Type anything into search box
Press Enter

Backtrace:
addr2line -C -f -i -p -e ./src/emacs.exe < ./emacs_backtrace.txt
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w32_backtrace at C:/other-projects/emacs/src/w32fns.c:11571
emacs_abort at C:/other-projects/emacs/src/w32fns.c:11610
terminate_due_to_signal at C:/other-projects/emacs/src/emacs.c:464
handle_fatal_signal at C:/other-projects/emacs/src/sysdep.c:1799
deliver_thread_signal at C:/other-projects/emacs/src/sysdep.c:1791
deliver_fatal_thread_signal at C:/other-projects/emacs/src/sysdep.c:1811
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rescale_for_division at C:/other-projects/emacs/src/floatfns.c:387
rounding_driver at C:/other-projects/emacs/src/floatfns.c:442
Ffloor at C:/other-projects/emacs/src/floatfns.c:536
funcall_subr at C:/other-projects/emacs/src/eval.c:3152
exec_byte_code at C:/other-projects/emacs/src/bytecode.c:813
funcall_lambda at C:/other-projects/emacs/src/eval.c:3241
funcall_general at C:/other-projects/emacs/src/eval.c:3033
Ffuncall at C:/other-projects/emacs/src/eval.c:3082
Fapply at C:/other-projects/emacs/src/eval.c:2754
funcall_subr at C:/other-projects/emacs/src/eval.c:3173
funcall_general at C:/other-projects/emacs/src/eval.c:3029
Ffuncall at C:/other-projects/emacs/src/eval.c:3082
?? ??:0
funcall_subr at C:/other-projects/emacs/src/eval.c:3150
funcall_general at C:/other-projects/emacs/src/eval.c:3029
Ffuncall at C:/other-projects/emacs/src/eval.c:3082
timer_check_2 at C:/other-projects/emacs/src/keyboard.c:4804
timer_check at C:/other-projects/emacs/src/keyboard.c:4869
readable_events at C:/other-projects/emacs/src/keyboard.c:3601
get_input_pending at C:/other-projects/emacs/src/keyboard.c:7872
detect_input_pending_run_timers at C:/other-projects/emacs/src/keyboard.c:11576
wait_reading_process_output at C:/other-projects/emacs/src/process.c:5856
sit_for at C:/other-projects/emacs/src/dispnew.c:6889
read_char at C:/other-projects/emacs/src/keyboard.c:2925
read_key_sequence at C:/other-projects/emacs/src/keyboard.c:10746
command_loop_1 at C:/other-projects/emacs/src/keyboard.c:1424
internal_condition_case at C:/other-projects/emacs/src/eval.c:1603
command_loop_2 at C:/other-projects/emacs/src/keyboard.c:1163
internal_catch at C:/other-projects/emacs/src/eval.c:1286
command_loop at C:/other-projects/emacs/src/keyboard.c:1141
recursive_edit_1 at C:/other-projects/emacs/src/keyboard.c:747
Frecursive_edit at C:/other-projects/emacs/src/keyboard.c:830
main at C:/other-projects/emacs/src/emacs.c:2635
__tmainCRTStartup at C:/M/B/src/mingw-w64/mingw-w64-crt/crt/crtexe.c:266
mainCRTStartup at C:/M/B/src/mingw-w64/mingw-w64-crt/crt/crtexe.c:185
__start at C:/other-projects/emacs/src/w32proc.c:158
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Notes:
Updating the rounding_driver function in ./src/floatfns.c from Emacs 26 resolved the issue.

diff --git a/src/floatfns.c b/src/floatfns.c
index 4492815c765..26c2e15da05 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -400,48 +400,79 @@ rescale_for_division (Lisp_Object n, mpz_t *t, int nscale, int dscale)

/* the rounding functions */

+static bool
+integer_value (Lisp_Object a)
+{
+ if (FLOATP (a))
+ {
+ double d = XFLOAT_DATA (a);
+ return d == floor (d) && isfinite (d);
+ }
+ return true;
+}
+
static Lisp_Object
-rounding_driver (Lisp_Object n, Lisp_Object d,
+rounding_driver (Lisp_Object arg, Lisp_Object divisor,
double (*double_round) (double),
void (*int_divide) (mpz_t, mpz_t const, mpz_t const),
EMACS_INT (*fixnum_divide) (EMACS_INT, EMACS_INT))
{
- CHECK_NUMBER (n);
+ CHECK_NUMBER (arg);

- if (NILP (d))
- return FLOATP (n) ? double_to_integer (double_round (XFLOAT_DATA (n))) : n;
-
- CHECK_NUMBER (d);
-
- int dscale = 0;
- if (FIXNUMP (d))
+ double d;
+ if (NILP (divisor))
{
- if (XFIXNUM (d) == 0)
- xsignal0 (Qarith_error);
-
- /* Divide fixnum by fixnum specially, for speed. */
- if (FIXNUMP (n))
- return make_int (fixnum_divide (XFIXNUM (n), XFIXNUM (d)));
+ if (! FLOATP (arg))
+ return arg;
+ d = XFLOAT_DATA (arg);
}
- else if (FLOATP (d))
+ else
{
- if (XFLOAT_DATA (d) == 0)
- xsignal0 (Qarith_error);
- dscale = double_integer_scale (XFLOAT_DATA (d));
- }
+ CHECK_NUMBER (divisor);
+ if (integer_value (arg) && integer_value (divisor))
+ {
+ /* Divide as integers. Converting to double might lose
+ info, even for fixnums; also see the FIXME below. */

- int nscale = FLOATP (n) ? double_integer_scale (XFLOAT_DATA (n)) : 0;
+ if (FLOATP (arg))
+ arg = double_to_integer (XFLOAT_DATA (arg));
+ if (FLOATP (divisor))
+ divisor = double_to_integer (XFLOAT_DATA (divisor));

- /* If the numerator is finite and the denominator infinite, the
- quotient is zero and there is no need to try the impossible task
- of rescaling the denominator. */
- if (dscale == DBL_MANT_DIG - DBL_MIN_EXP + 1 && nscale < dscale)
- return make_fixnum (0);
+ if (FIXNUMP (divisor))
+ {
+ if (XFIXNUM (divisor) == 0)
+ xsignal0 (Qarith_error);
+ if (FIXNUMP (arg))
+ return make_int (fixnum_divide (XFIXNUM (arg),
+ XFIXNUM (divisor)));
+ }
+ int_divide (mpz[0],
+ ,*bignum_integer (&mpz[0], arg),
+ ,*bignum_integer (&mpz[1], divisor));
+ return make_integer_mpz ();
+ }

- int_divide (mpz[0],
- *rescale_for_division (n, &mpz[0], nscale, dscale),
- *rescale_for_division (d, &mpz[1], dscale, nscale));
- return make_integer_mpz ();
+ double f1 = XFLOATINT (arg);
+ double f2 = XFLOATINT (divisor);
+ if (! IEEE_FLOATING_POINT && f2 == 0)
+ xsignal0 (Qarith_error);
+ /* FIXME: This division rounds, so the result is double-rounded. */
+ d = f1 / f2;
+ }
+
+ /* Round, coarsely test for fixnum overflow before converting to
+ EMACS_INT (to avoid undefined C behavior), and then exactly test
+ for overflow after converting (as FIXNUM_OVERFLOW_P is inaccurate
+ on floats). */
+ double dr = double_round (d);
+ if (fabs (dr) < 2 * (MOST_POSITIVE_FIXNUM + 1))
+ {
+ EMACS_INT ir = dr;
+ if (! FIXNUM_OVERFLOW_P (ir))
+ return make_fixnum (ir);
+ }
+ return double_to_integer (dr);
}

static EMACS_INT