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* src/data.c (arithcompare): Add comments.

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This commit is contained in:
Paul Eggert 2017-03-08 13:43:16 -08:00
parent de610c4b67
commit 84d415e94c
1 changed files with 18 additions and 4 deletions
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22
src/data.c
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@ -2404,9 +2404,11 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
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. Regardless, set I1 and I2
to integers that break ties if the floating point comparison is
either not done or reports equality. */
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
equality. */
if (FLOATP (num1))
{
@ -2417,7 +2419,17 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
f2 = XFLOAT_DATA (num2);
}
else
i1 = f2 = i2 = XINT (num2);
{
/* Compare a float NUM1 to an integer NUM2 by converting the
integer I2 (i.e., NUM2) to the double F2 (a conversion that
can round on some platforms, if I2 is large enough), and then
converting F2 back to the integer I1 (a conversion that is
always exact), so that I1 exactly equals ((double) NUM2). If
floating-point comparison reports a tie, NUM1 = F1 = F2 = I1
(exactly) so I1 - I2 = NUM1 - NUM2 (exactly), so comparing I1
to I2 will break the tie correctly. */
i1 = f2 = i2 = XINT (num2);
}
fneq = f1 != f2;
}
else
@ -2425,6 +2437,8 @@ arithcompare (Lisp_Object num1, Lisp_Object num2,
i1 = XINT (num1);
if (FLOATP (num2))
{
/* Compare an integer NUM1 to a float NUM2. This is the
converse of comparing float to integer (see above). */
i2 = f1 = i1;
f2 = XFLOAT_DATA (num2);
fneq = f1 != f2;