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Port better to x86 -fexcess-precision=fast

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Problem reported by Eli Zaretskii in:
https://lists.gnu.org/r/emacs-devel/2018-08/msg00380.html
* src/data.c (arithcompare): Work around incompatibility
between gcc -fexcess-precision=fast and the C standard on x86,
by capturing the results of floating-point comparisons before
the excess precision spontaneously decays.  Although this fix
might not work in general, it does work here and is probably
good enough for the platforms we care about.

(cherry picked from commit a84cef9095)
This commit is contained in:
Paul Eggert 2018-08-12 15:28:20 -07:00 • committed by Eli Zaretskii
parent 34e75c144e
commit f882de8b80
1 changed files with 29 additions and 14 deletions
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43
src/data.c
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@ -2411,17 +2411,20 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
{
double f1, f2;
EMACS_INT i1, i2;
bool fneq;
bool lt, eq, gt;
bool test;
CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (num1);
CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (num2);
/* If either arg is floating point, set F1 and F2 to the 'double'
approximations of the two arguments, and set FNEQ if floating-point
comparison reports that F1 is not equal to F2, possibly because F1
or F2 is a NaN. Regardless, set I1 and I2 to integers that break
ties if the floating-point comparison is either not done or reports
approximations of the two arguments, and set LT, EQ, and GT to
the <, ==, > floating-point comparisons of F1 and F2
respectively, taking care to avoid problems if either is a NaN,
and trying to avoid problems on platforms where variables (in
violation of the C standard) can contain excess precision.
Regardless, set I1 and I2 to integers that break ties if the
floating-point comparison is either not done or reports
equality. */
if (FLOATP (num1))
@ -2444,7 +2447,9 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
to I2 will break the tie correctly. */
i1 = f2 = i2 = XINT (num2);
}
fneq = f1 != f2;
lt = f1 < f2;
eq = f1 == f2;
gt = f1 > f2;
}
else
{
@ -2455,39 +2460,49 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
converse of comparing float to integer (see above). */
i2 = f1 = i1;
f2 = XFLOAT_DATA (num2);
fneq = f1 != f2;
lt = f1 < f2;
eq = f1 == f2;
gt = f1 > f2;
}
else
{
i2 = XINT (num2);
fneq = false;
eq = true;
}
}
if (eq)
{
/* Break a floating-point tie by comparing the integers. */
lt = i1 < i2;
eq = i1 == i2;
gt = i1 > i2;
}
switch (comparison)
{
case ARITH_EQUAL:
test = !fneq && i1 == i2;
test = eq;
break;
case ARITH_NOTEQUAL:
test = fneq || i1 != i2;
test = !eq;
break;
case ARITH_LESS:
test = fneq ? f1 < f2 : i1 < i2;
test = lt;
break;
case ARITH_LESS_OR_EQUAL:
test = fneq ? f1 <= f2 : i1 <= i2;
test = lt | eq;
break;
case ARITH_GRTR:
test = fneq ? f1 > f2 : i1 > i2;
test = gt;
break;
case ARITH_GRTR_OR_EQUAL:
test = fneq ? f1 >= f2 : i1 >= i2;
test = gt | eq;
break;
default: