Hi!
The following testcase shows that while at runtime we handle conversions
between _Decimal{64,128} and large _BitInt correctly, at compile time we
mishandle them in both directions, in one direction we end up in ICE in
decimal_from_integer callee because the char buffer is too short for the
needed number of decimal digits, in the conversion of dfp to large _BitInt
we return 0 in the wide_int.
The following patch fixes the ICE by using larger buffer (XALLOCAVEC
allocated, it will be never larger than 65536 / 3 bytes) in the larger
_BitInt case, and the other direction by setting exponent to exp % 19
and instead multiplying the result by needed powers of 10^19 (10^19 chosen
as largest power of ten that can fit into UHWI).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk/15.2/14.4?
2025-06-17 Jakub Jelinek <ja...@redhat.com>
PR middle-end/120631
* real.cc (decimal_from_integer): Add digits argument, if larger than
256, use XALLOCAVEC allocated buffer.
(real_from_integer): Pass val_in's precision divided by 3 to
decimal_from_integer.
* dfp.cc (decimal_real_to_integer): For precision > 128 if finite
and exponent is large, decrease exponent and multiply resulting
wide_int by powers of 10^19.
* gcc.dg/dfp/bitint-9.c: New test.
--- gcc/real.cc.jj 2025-06-05 15:47:08.313244971 +0200
+++ gcc/real.cc 2025-06-17 14:40:16.565601561 +0200
@@ -101,7 +101,7 @@ static int do_compare (const REAL_VALUE_
static void do_fix_trunc (REAL_VALUE_TYPE *, const REAL_VALUE_TYPE *);
static unsigned long rtd_divmod (REAL_VALUE_TYPE *, REAL_VALUE_TYPE *);
-static void decimal_from_integer (REAL_VALUE_TYPE *);
+static void decimal_from_integer (REAL_VALUE_TYPE *, int);
static void decimal_integer_string (char *, const REAL_VALUE_TYPE *,
size_t);
@@ -2309,7 +2309,9 @@ real_from_integer (REAL_VALUE_TYPE *r, f
}
if (fmt.decimal_p ())
- decimal_from_integer (r);
+ /* We need at most one decimal digits for each 3 bits of input
+ precision. */
+ decimal_from_integer (r, val_in.get_precision () / 3);
if (fmt)
real_convert (r, fmt, r);
}
@@ -2364,12 +2366,21 @@ decimal_integer_string (char *str, const
/* Convert a real with an integral value to decimal float. */
static void
-decimal_from_integer (REAL_VALUE_TYPE *r)
+decimal_from_integer (REAL_VALUE_TYPE *r, int digits)
{
char str[256];
- decimal_integer_string (str, r, sizeof (str) - 1);
- decimal_real_from_string (r, str);
+ if (digits <= 256)
+ {
+ decimal_integer_string (str, r, sizeof (str) - 1);
+ decimal_real_from_string (r, str);
+ }
+ else
+ {
+ char *s = XALLOCAVEC (char, digits);
+ decimal_integer_string (s, r, digits - 1);
+ decimal_real_from_string (r, s);
+ }
}
/* Returns 10**2**N. */
--- gcc/dfp.cc.jj 2025-04-08 14:08:50.669289967 +0200
+++ gcc/dfp.cc 2025-06-17 17:28:25.101792744 +0200
@@ -619,11 +619,21 @@ decimal_real_to_integer (const REAL_VALU
decNumber dn, dn2, dn3;
REAL_VALUE_TYPE to;
char string[256];
+ int scale = 0;
decContextDefault (&set, DEC_INIT_DECIMAL128);
set.traps = 0;
set.round = DEC_ROUND_DOWN;
decimal128ToNumber ((const decimal128 *) r->sig, &dn);
+ if (precision > 128 && decNumberIsFinite (&dn) && dn.exponent > 19)
+ {
+ /* libdecNumber doesn't really handle too large integers.
+ So when precision is large and exponent as well, trim the
+ exponent and adjust the resulting wide_int by multiplying
+ it multiple times with 10^19. */
+ scale = dn.exponent / 19;
+ dn.exponent %= 19;
+ }
decNumberToIntegralValue (&dn2, &dn, &set);
decNumberZero (&dn3);
@@ -633,7 +643,44 @@ decimal_real_to_integer (const REAL_VALU
function. */
decNumberToString (&dn, string);
real_from_string (&to, string);
- return real_to_integer (&to, fail, precision);
+ bool failp = false;
+ wide_int w = real_to_integer (&to, &failp, precision);
+ if (failp)
+ *fail = true;
+ if (scale && !failp)
+ {
+ wide_int wm = wi::uhwi (HOST_WIDE_INT_UC (10000000000000000000),
+ w.get_precision ());
+ bool isneg = wi::neg_p (w);
+ if (isneg)
+ w = -w;
+ enum wi::overflow_type ovf = wi::OVF_NONE;
+ do
+ {
+ if (scale & 1)
+ {
+ w = wi::umul (w, wm, &ovf);
+ if (ovf)
+ break;
+ }
+ scale >>= 1;
+ if (!scale)
+ break;
+ wm = wi::umul (wm, wm, &ovf);
+ }
+ while (!ovf);
+ if (ovf)
+ {
+ *fail = true;
+ if (isneg)
+ return wi::set_bit_in_zero (precision - 1, precision);
+ else
+ return ~wi::set_bit_in_zero (precision - 1, precision);
+ }
+ if (isneg)
+ w = -w;
+ }
+ return w;
}
/* Perform the decimal floating point operation described by CODE.
--- gcc/testsuite/gcc.dg/dfp/bitint-9.c.jj 2025-06-17 17:30:13.271374809
+0200
+++ gcc/testsuite/gcc.dg/dfp/bitint-9.c 2025-06-17 14:53:36.997994620 +0200
@@ -0,0 +1,29 @@
+/* PR middle-end/120631 */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-O2" } */
+
+#if __BITINT_MAXWIDTH__ >= 2048
+_Decimal128 a =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dl;
+_BitInt(2048) b =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+_Decimal64 c =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dd;
+_BitInt(1536) d =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+#endif
+
+int
+main ()
+{
+#if __BITINT_MAXWIDTH__ >= 2048
+ if (a != b || (_BitInt(2048)) a != b || c != d || (_BitInt(1536)) c != d)
+ __builtin_abort ();
+ _Decimal128 e =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dl;
+ _BitInt(2048) f =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+ _Decimal128 g =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+ _BitInt(2048) h =
123456789135792468012345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dl;
+ _Decimal64 i =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dd;
+ _BitInt(1536) j =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+ _Decimal64 k =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000wb;
+ _BitInt(1536) l =
123456789135790000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0dd;
+ if (e != g || f != h || i != k || j != l)
+ __builtin_abort ();
+#endif
+}
Jakub
