X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=numeric.c;h=d15fdbdd75fe3f56c5bc1358a25ddc5ffabbf57c;hb=1cc8b4c566f7901a54e4b576f09608beb4c81f86;hp=8d94975f1df70ee869acce098f1e13af26a599af;hpb=a24374368d9ca399370d0bbf60ebc0aa16225436;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/numeric.c b/numeric.c
index 8d94975..d15fdbd 100644
--- a/numeric.c
+++ b/numeric.c
@@ -572,24 +572,43 @@ S_mulexp10(NV value, I32 exponent)
 	negative = 1;
 	exponent = -exponent;
     }
-#ifdef __VAX /* avoid %SYSTEM-F-FLTOVF_F sans VAXC$ESTABLISH */
-#  if defined(__DECC_VER) && __DECC_VER <= 50390006
-    /* __F_FLT_MAX_10_EXP - 5 == 33 */
+
+    /* On OpenVMS VAX we by default use the D_FLOAT double format,
+     * and that format does not have *easy* capabilities [1] for
+     * overflowing doubles 'silently' as IEEE fp does.  We also need 
+     * to support G_FLOAT on both VAX and Alpha, and though the exponent 
+     * range is much larger than D_FLOAT it still doesn't do silent 
+     * overflow.  Therefore we need to detect early whether we would 
+     * overflow (this is the behaviour of the native string-to-float 
+     * conversion routines, and therefore of native applications, too).
+     *
+     * [1] Trying to establish a condition handler to trap floating point
+     *     exceptions is not a good idea. */
+#if defined(VMS) && !defined(__IEEE_FP) && defined(NV_MAX_10_EXP)
     if (!negative &&
-          (log10(value) + exponent) >= (__F_FLT_MAX_10_EXP - 5))
+        (log10(value) + exponent) >= (NV_MAX_10_EXP))
         return NV_MAX;
-#  endif
 #endif
-#if defined(__alpha) && defined(__unix__)
+
+    /* In UNICOS and in certain Cray models (such as T90) there is no
+     * IEEE fp, and no way at all from C to catch fp overflows gracefully.
+     * There is something you can do if you are willing to use some
+     * inline assembler: the instruction is called DFI-- but that will
+     * disable *all* floating point interrupts, a little bit too large
+     * a hammer.  Therefore we need to catch potential overflows before
+     * it's too late. */
+#if defined(_UNICOS) && defined(NV_MAX_10_EXP)
     if (!negative &&
-	(log10(value) + exponent) >= (DBL_MAX_10_EXP))
-        return NV_INF;
+	(log10(value) + exponent) >= NV_MAX_10_EXP)
+        return NV_MAX;
 #endif
+
     for (bit = 1; exponent; bit <<= 1) {
 	if (exponent & bit) {
 	    exponent ^= bit;
 	    result *= power;
 	}
+	/* Floating point exceptions are supposed to be turned off. */
 	power *= power;
     }
     return negative ? value / result : value * result;