Fix CPU hog function

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: build
       run: |
-           brew install autoconf automake libtool
+           brew install autoconf automake libtool txt2man
            ./autogen.sh
            ./configure
            make
@@ -30,6 +30,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+    - name: install build dependencies
+      run: |
+           sudo apt-get update
+           sudo env DEBIAN_FRONTEND=noninteractive apt-get install -qy txt2man
     - name: first_build
       run: |
            ./autogen.sh

Makefile.am

@@ -8,3 +8,13 @@ distclean-local:
 	rm -rf autom4te.cache
 	rm -f  aclocal.m4 compile config.* configure depcomp INSTALL install-sh \
                Makefile.in missing src/Makefile.in test-driver test/Makefile.in
+
+man/stress.1: man/stress.txt
+	txt2man -t stress \
+		  -r stress-@PACKAGE_VERSION@ \
+		  -d "@RELEASE_DAY@" \
+		  -s 1 \
+		  -v "tool to impose load on and stress test systems" \
+		  $< > $@
+
+.PHONY: distclean-local

configure.ac

@@ -1,5 +1,6 @@
 AC_PREREQ([2.69])
 AC_INIT([stress], [1.0.7], [https://github.com/resurrecting-open-source-projects/stress/issues])
+AC_SUBST([RELEASE_DAY], ["21 Jan 2023"], [Day of release (used in man page)])
 AC_CONFIG_SRCDIR([src/stress.c])
 AC_CONFIG_HEADERS([config.h])
 AM_INIT_AUTOMAKE
@@ -17,6 +18,9 @@ AC_FUNC_FORK
 AC_FUNC_MALLOC
 AC_CHECK_FUNCS([alarm sqrt strerror])
 
+# Checks for build helpers
+AC_CHECK_PROG(TXT2MAN_CHECK, txt2man, yes)
+AS_IF([test x"$TXT2MAN_CHECK" != x"yes"], [AC_MSG_ERROR([txt2man tool needed to generate man page])])
 # Special functions
 AC_ARG_ENABLE([static],
                AS_HELP_STRING([--enable-static],

man/stress.txt

@@ -23,7 +23,8 @@ OPTIONS
  -n, --dry-run      Show what would have been done.
  -t, --timeout <N>  Timeout after N seconds. This option is ignored by -n.
  --backoff <N>      Wait for factor of microseconds before starting work.
- -c, --cpu <N>      Spawn N workers spinning on sqrt().
+ -c, --cpu <N>      Spawn N workers spinning on pseudo-random number generation
+                    and sqrt().
  -i, --io <N>       Spawn N workers spinning on sync().
  -m, --vm <N>       Spawn N workers spinning on malloc()/free().
  --vm-bytes <B>     Malloc B bytes per vm worker (default is 256MB).
@@ -39,7 +40,8 @@ OPTIONS
 EXAMPLES
  The simple case is that you just want to bring the system load average up to an
  arbitrary value. The following forks 13 processes, each of which spins in a
- tight loop calculating the sqrt() of a random number acquired with rand().
+ tight loop calculating the sqrt() of a random number acquired from a fixed-seed
+ pseudo-random number generator (xoroshiro128+).
 
     stress -c 13
 

src/stress.c

@@ -3,6 +3,7 @@
  * Copyright 2001-2010 Amos Waterland <[email protected]>
  * Copyright 2021-2023 Joao Eriberto Mota Filho <[email protected]>
  * Copyright 2023      Vratislav Bendel <[email protected]>
+ * Copyright 2025      Marcus Müller <[email protected]>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -23,6 +24,7 @@
 #include <errno.h>
 #include <libgen.h>
 #include <math.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -479,9 +481,47 @@ void worker_init(void)
 int
 hogcpu (void)
 {
-    while (1)
-        sqrt (rand ());
-
+    /* initial state for PRNG */
+    static uint32_t s[] = {
+        4 /* chosen by fair dice roll */,
+        42 /* the answer */,
+        3 /* pi */,
+        0xCAFECA4E /* because who doesn't like cake? */
+    };
+    while (1) {
+        /* START xoroshirp128plus:
+         Written in 2018 by David Blackman and Sebastiano Vigna ([email protected])
+
+        To the extent possible under law, the author has dedicated all copyright
+        and related and neighboring rights to this software to the public domain
+        worldwide.
+
+        Permission to use, copy, modify, and/or distribute this software for any
+        purpose with or without fee is hereby granted.
+
+        THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+        WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+        MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+        ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+        WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+        ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
+        IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+        */
+
+        const uint32_t result = s[0] + s[3];
+        const uint32_t t = s[1] << 9;
+
+        s[2] ^= s[0];
+        s[3] ^= s[1];
+        s[1] ^= s[2];
+        s[0] ^= s[3];
+
+        s[2] ^= t;
+
+        s[3] = (s[3] << 11) | (s[3]>> (32-11));
+        /* END xoroshirp128plus */
+        volatile double value = sqrt ((double)(result));
+    }
     return 0;
 }
 
@@ -762,7 +802,8 @@ usage (int status)
         " -n, --dry-run      show what would have been done\n"
         " -t, --timeout N    timeout after N seconds\n"
         "     --backoff N    wait factor of N microseconds before work starts\n"
-        " -c, --cpu N        spawn N workers spinning on sqrt()\n"
+        " -c, --cpu N        spawn N workers spinning on pseudo-random number generation\n"
+        "                    and sqrt()\n"
         " -i, --io N         spawn N workers spinning on sync()\n"
         " -m, --vm N         spawn N workers spinning on malloc()/free()\n"
         "     --vm-bytes B   malloc B bytes per vm worker (default is 256MB)\n"