Thu May 9 22:38:29 2024 UTC (22d)

tests/lib/libc/stdio/t_printf: Fix another rounding error.

Noted by kre.

This doesn't break a passing test or fix a failed test, at least on
x86 -- our printf produces `0x1.533p+3' for the double case and
`0xa.99ap+0' for the long double case.  But of the hexadecimal number
literals that that start with 0x5 having three hexadigits to the
right of the fractional point, 0x5.4cdp+1 closest to the IEEE 754
binary64, VAX D, x86 extended precision, and IEEE 754 binary128
floating-point numbers closest to 10.6.

The reason is that the number 10.6 (or the nearest floating-point
number in any format with enough precision) is:

101.0100 1100 1100|1100... * 2^1 = 0x5.4cc|c...p+1

If we round at the vertical bar to the _nearest_ output with three
hexadigits of precision, the result is:

101.0100 1100 1101 * 2^1 = 0x5.4cdp+1


(riastradh)

diff -r1.15 -r1.16 src/tests/lib/libc/stdio/t_printf.c

--- src/tests/lib/libc/stdio/t_printf.c 2024/05/09 12:24:24	1.15
+++ src/tests/lib/libc/stdio/t_printf.c 2024/05/09 22:38:29	1.16

 @@ -1,14 +1,14 @@
-/* $NetBSD: t_printf.c,v 1.15 2024/05/09 12:24:24 riastradh Exp $ */
+/* $NetBSD: t_printf.c,v 1.16 2024/05/09 22:38:29 riastradh Exp $ */
 /*-
  * Copyright (c) 2010 The NetBSD Foundation, Inc.
  * All rights reserved.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
 @@ -185,52 +185,52 @@ ATF_TC_BODY(sprintf_zeropad, tc)
 ATF_TC(snprintf_double_a);
 ATF_TC_HEAD(snprintf_double_a, tc)
+{
 	atf_tc_set_md_var(tc, "descr", "Test printf a format");
+}
 ATF_TC_BODY(snprintf_double_a, tc)
+{
 	char buf[1000];
 	snprintf(buf, sizeof buf, "%.3a", (double)10.6);
 	ATF_CHECK_MSG((strcmp(buf, "0x1.533p+3") == 0 ||
 		strcmp(buf, "0x2.a66p+2") == 0 ||
-		strcmp(buf, "0x5.4ccp+1") == 0 ||
+		strcmp(buf, "0x5.4cdp+1") == 0 ||
 		strcmp(buf, "0xa.99ap+0") == 0),
 	    "buf=%s", buf);
 	snprintf(buf, sizeof buf, "%a", (double)0.125);
 	ATF_CHECK_MSG((strcmp(buf, "0x1p-3") == 0 ||
 		strcmp(buf, "0x2p-4") == 0 ||
 		strcmp(buf, "0x4p-5") == 0 ||
 		strcmp(buf, "0x8p-6") == 0),
 	    "buf=%s", buf);
+}
 ATF_TC(snprintf_long_double_a);
 ATF_TC_HEAD(snprintf_long_double_a, tc)
+{
 	atf_tc_set_md_var(tc, "descr", "Test printf La format");
+}
 ATF_TC_BODY(snprintf_long_double_a, tc)
+{
 	char buf[1000];
 	snprintf(buf, sizeof buf, "%.3La", 10.6L);
 	ATF_CHECK_MSG((strcmp(buf, "0x1.533p+3") == 0 ||
 		strcmp(buf, "0x2.a66p+2") == 0 ||
-		strcmp(buf, "0x5.4ccp+1") == 0 ||
+		strcmp(buf, "0x5.4cdp+1") == 0 ||
 		strcmp(buf, "0xa.99ap+0") == 0),
 	    "buf=%s", buf);
 	snprintf(buf, sizeof buf, "%La", 0.125L);
 	ATF_CHECK_MSG((strcmp(buf, "0x1p-3") == 0 ||
 		strcmp(buf, "0x2p-4") == 0 ||
 		strcmp(buf, "0x4p-5") == 0 ||
 		strcmp(buf, "0x8p-6") == 0),
 	    "buf=%s", buf);
 #if LDBL_MAX_EXP >= 16384 && LDBL_MANT_DIG >= 64
 	snprintf(buf, sizeof buf, "%La", -0xc.ecececececececep+3788L);
 	ATF_CHECK_MSG((strcmp(buf, "-0x1.9d9d9d9d9d9d9d9cp+3791") == 0 ||