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Configure: notes on the m68881 extended precision format
authorJarkko Hietaniemi <jhi@iki.fi>
Thu, 17 Dec 2015 02:57:31 +0000 (21:57 -0500)
committerJarkko Hietaniemi <jhi@iki.fi>
Fri, 18 Dec 2015 12:21:03 +0000 (07:21 -0500)
Configure

index 2a4ee8c..0e71b4b 100755 (executable)
--- a/Configure
+++ b/Configure
@@ -6967,7 +6967,15 @@ int main() {
     exit(0);
   }
   if (b[0] == 0xBF && b[9] == 0xCD) {
     exit(0);
   }
   if (b[0] == 0xBF && b[9] == 0xCD) {
-    /* is there ever big-endian 80-bit, really? */
+    /* Is there ever big-endian 80-bit, really?
+     *
+     * The Motorola 68881 had another "extended precision" format:
+     * sign:1 exp:15 zero:16 integer:1 mantissa:63
+     * for total of 96 bits of bytes.  The zero bits were unused.
+     * See "M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL" for more details.
+     * If it ever becomes relevant, this format should be allocated
+     * a new doublekind code since it's quite different from the Intel x87.
+     */
     printf("4\n");
     exit(0);
   }
     printf("4\n");
     exit(0);
   }