[git commit master] ash: factor out $RANDOM support

Denys Vlasenko vda.linux at googlemail.com
Fri Oct 9 18:59:39 UTC 2009


commit: http://git.busybox.net/busybox/commit/?id=3ea2e82dc7b32703f5043c3b30b049905a0d07aa
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

function                                             old     new   delta
next_random                                            -      46     +46
ash_main                                            1361    1356      -5
change_random                                        132      97     -35
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/2 up/down: 46/-40)              Total: 6 bytes

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 shell/Kbuild   |    3 +++
 shell/ash.c    |   46 ++++++++++++++++++----------------------------
 shell/random.c |   37 +++++++++++++++++++++++++++++++++++++
 shell/random.h |   19 +++++++++++++++++++
 4 files changed, 77 insertions(+), 28 deletions(-)
 create mode 100644 shell/random.c
 create mode 100644 shell/random.h

diff --git a/shell/Kbuild b/shell/Kbuild
index 4d4741e..03960a8 100644
--- a/shell/Kbuild
+++ b/shell/Kbuild
@@ -8,4 +8,7 @@ lib-y:=
 lib-$(CONFIG_ASH)      += ash.o ash_ptr_hack.o
 lib-$(CONFIG_HUSH)     += hush.o match.o
 lib-$(CONFIG_CTTYHACK) += cttyhack.o
+
 lib-$(CONFIG_SH_MATH_SUPPORT) += math.o
+lib-$(CONFIG_ASH_RANDOM_SUPPORT) += random.o
+lib-$(CONFIG_HUSH_RANDOM_SUPPORT) += random.o
diff --git a/shell/ash.c b/shell/ash.c
index f2d372f..6ce6215 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -51,16 +51,19 @@
 #include <setjmp.h>
 #include <fnmatch.h>
 #include "math.h"
+#if ENABLE_ASH_RANDOM_SUPPORT
+# include "random.h"
+#endif
 
 #if defined SINGLE_APPLET_MAIN
 /* STANDALONE does not make sense, and won't compile */
-#undef CONFIG_FEATURE_SH_STANDALONE
-#undef ENABLE_FEATURE_SH_STANDALONE
-#undef IF_FEATURE_SH_STANDALONE
-#undef IF_NOT_FEATURE_SH_STANDALONE(...)
-#define ENABLE_FEATURE_SH_STANDALONE 0
-#define IF_FEATURE_SH_STANDALONE(...)
-#define IF_NOT_FEATURE_SH_STANDALONE(...) __VA_ARGS__
+# undef CONFIG_FEATURE_SH_STANDALONE
+# undef ENABLE_FEATURE_SH_STANDALONE
+# undef IF_FEATURE_SH_STANDALONE
+# undef IF_NOT_FEATURE_SH_STANDALONE(...)
+# define ENABLE_FEATURE_SH_STANDALONE 0
+# define IF_FEATURE_SH_STANDALONE(...)
+# define IF_NOT_FEATURE_SH_STANDALONE(...) __VA_ARGS__
 #endif
 
 #ifndef PIPE_BUF
@@ -197,9 +200,7 @@ struct globals_misc {
 
 	/* Rarely referenced stuff */
 #if ENABLE_ASH_RANDOM_SUPPORT
-	/* Random number generators */
-	int32_t random_galois_LFSR; /* Galois LFSR (fast but weak). signed! */
-	uint32_t random_LCG;        /* LCG (fast but weak) */
+	random_t random_gen;
 #endif
 	pid_t backgndpid;        /* pid of last background process */
 	smallint job_warning;    /* user was warned about stopped jobs (can be 2, 1 or 0). */
@@ -224,8 +225,7 @@ extern struct globals_misc *const ash_ptr_to_globals_misc;
 #define gotsig      (G_misc.gotsig     )
 #define trap        (G_misc.trap       )
 #define trap_ptr    (G_misc.trap_ptr   )
-#define random_galois_LFSR (G_misc.random_galois_LFSR)
-#define random_LCG         (G_misc.random_LCG        )
+#define random_gen  (G_misc.random_gen )
 #define backgndpid  (G_misc.backgndpid )
 #define job_warning (G_misc.job_warning)
 #define INIT_G_misc() do { \
@@ -10075,28 +10075,18 @@ change_random(const char *value)
 	/* Another example - taps at 32 31 30 10: */
 	/* MASK = 0x00400007 */
 
+	uint32_t t;
+
 	if (value == NULL) {
 		/* "get", generate */
-		uint32_t t;
-
-		/* LCG has period of 2^32 and alternating lowest bit */
-		random_LCG = 1664525 * random_LCG + 1013904223;
-		/* Galois LFSR has period of 2^32-1 = 3 * 5 * 17 * 257 * 65537 */
-		t = (random_galois_LFSR << 1);
-		if (random_galois_LFSR < 0) /* if we just shifted 1 out of msb... */
-			t ^= MASK;
-		random_galois_LFSR = t;
-		/* Both are weak, combining them gives better randomness
-		 * and ~2^64 period. & 0x7fff is probably bash compat
-		 * for $RANDOM range. Combining with subtraction is
-		 * just for fun. + and ^ would work equally well. */
-		t = (t - random_LCG) & 0x7fff;
+		t = next_random(&random_gen);
 		/* set without recursion */
 		setvar(vrandom.text, utoa(t), VNOFUNC);
 		vrandom.flags &= ~VNOFUNC;
 	} else {
 		/* set/reset */
-		random_galois_LFSR = random_LCG = strtoul(value, NULL, 10);
+		t = strtoul(value, NULL, 10);
+		INIT_RANDOM_T(&random_gen, (t ? t : 1), t);
 	}
 }
 #endif
@@ -13271,7 +13261,7 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
 #if ENABLE_ASH_RANDOM_SUPPORT
 	/* Can use monotonic_ns() for better randomness but for now it is
 	 * not used anywhere else in busybox... so avoid bloat */
-	random_galois_LFSR = random_LCG = rootpid + monotonic_us();
+	INIT_RANDOM_T(&random_gen, rootpid, monotonic_us());
 #endif
 	init();
 	setstackmark(&smark);
diff --git a/shell/random.c b/shell/random.c
new file mode 100644
index 0000000..a4dce84
--- /dev/null
+++ b/shell/random.c
@@ -0,0 +1,37 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * $RANDOM support.
+ *
+ * Copyright (C) 2008 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+#include "random.h"
+
+uint32_t FAST_FUNC
+next_random(random_t *rnd)
+{
+	/* Galois LFSR parameter */
+	/* Taps at 32 31 29 1: */
+	enum { MASK = 0x8000000b };
+	/* Another example - taps at 32 31 30 10: */
+	/* MASK = 0x00400007 */
+
+	uint32_t t;
+
+	/* LCG has period of 2^32 and alternating lowest bit */
+	rnd->LCG = 1664525 * rnd->LCG + 1013904223;
+	/* Galois LFSR has period of 2^32-1 = 3 * 5 * 17 * 257 * 65537 */
+	t = (rnd->galois_LFSR << 1);
+	if (rnd->galois_LFSR < 0) /* if we just shifted 1 out of msb... */
+		t ^= MASK;
+	rnd->galois_LFSR = t;
+	/* Both are weak, combining them gives better randomness
+	 * and ~2^64 period. & 0x7fff is probably bash compat
+	 * for $RANDOM range. Combining with subtraction is
+	 * just for fun. + and ^ would work equally well. */
+	t = (t - rnd->LCG) & 0x7fff;
+
+	return t;
+}
diff --git a/shell/random.h b/shell/random.h
new file mode 100644
index 0000000..2d29a60
--- /dev/null
+++ b/shell/random.h
@@ -0,0 +1,19 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * $RANDOM support.
+ *
+ * Copyright (C) 2008 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+
+typedef struct random_t {
+	/* Random number generators */
+	int32_t galois_LFSR; /* Galois LFSR (fast but weak). signed! */
+	uint32_t LCG;        /* LCG (fast but weak) */
+} random_t;
+
+#define INIT_RANDOM_T(rnd, nonzero, v) \
+	((rnd)->galois_LFSR = (nonzero), (rnd)->LCG = (v))
+
+uint32_t next_random(random_t *rnd) FAST_FUNC;
-- 
1.6.3.3



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