Merge glibc random, which gets us a much better RNG and a

reentrant one as well.  It is not much bigger than what we
had, so...
 -Erik

3 files changed, 607 insertions, 24 deletions

diff --git a/libc/stdlib/Makefile b/libc/stdlib/Makefile
index 8d7f949df..71136c2fa 100644
--- a/libc/stdlib/Makefile
+++ b/libc/stdlib/Makefile
@@ -38,7 +38,7 @@ MSRC2=atexit.c
 MOBJ2=atexit.o on_exit.o __exit_handler.o exit.o
 
 CSRC =	abort.c getenv.c mktemp.c qsort.c realpath.c bsearch.c \
-	mkstemp.c putenv.c rand.c random.c setenv.c system.c div.c \
+	mkstemp.c putenv.c rand.c random.c random_r.c setenv.c system.c div.c \
 	ldiv.c getpt.c ptsname.c grantpt.c unlockpt.c gcvt.c
 CSRC+=  drand48.c drand48-iter.c drand48_r.c erand48.c erand48_r.c \
 	jrand48.c jrand48_r.c lrand48.c lrand48_r.c mrand48.c mrand48_r.c \
diff --git a/libc/stdlib/random.c b/libc/stdlib/random.c
index cbd4206ae..bc20d1e1b 100644
--- a/libc/stdlib/random.c
+++ b/libc/stdlib/random.c
@@ -1,37 +1,255 @@
-#include <stdlib.h>
+/*
+ * Copyright (c) 1983 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that the above copyright notice and this paragraph are
+ * duplicated in all such forms and that any documentation,
+ * advertising materials, and other materials related to such
+ * distribution and use acknowledge that the software was developed
+ * by the University of California, Berkeley.  The name of the
+ * University may not be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
 
 /*
- * This generator is a combination of three linear congruential generators
- * with periods or 2^15-405, 2^15-1041 and 2^15-1111. It has a period that
- * is the product of these three numbers.
+ * This is derived from the Berkeley source:
+ *	@(#)random.c	5.5 (Berkeley) 7/6/88
+ * It was reworked for the GNU C Library by Roland McGrath.
+ * Rewritten to use reentrant functions by Ulrich Drepper, 1995.
  */
 
-static long int seed1 = 1;
-static long int seed2 = 1;
-static long int seed3 = 1;
+#define _GNU_SOURCE
+#include <features.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+#ifdef __UCLIBC_HAS_THREADS__
+#include <pthread.h>
+/* POSIX.1c requires that there is mutual exclusion for the `rand' and
+   `srand' functions to prevent concurrent calls from modifying common
+   data.  */
+static pthread_mutex_t lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
+#else
+#define pthread_mutex_lock(x)
+#define pthread_mutex_unlock(x)
+#endif
+
+/* An improved random number generation package.  In addition to the standard
+   rand()/srand() like interface, this package also has a special state info
+   interface.  The initstate() routine is called with a seed, an array of
+   bytes, and a count of how many bytes are being passed in; this array is
+   then initialized to contain information for random number generation with
+   that much state information.  Good sizes for the amount of state
+   information are 32, 64, 128, and 256 bytes.  The state can be switched by
+   calling the setstate() function with the same array as was initialized
+   with initstate().  By default, the package runs with 128 bytes of state
+   information and generates far better random numbers than a linear
+   congruential generator.  If the amount of state information is less than
+   32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
+   state information is treated as an array of longs; the zeroth element of
+   the array is the type of R.N.G. being used (small integer); the remainder
+   of the array is the state information for the R.N.G.  Thus, 32 bytes of
+   state information will give 7 longs worth of state information, which will
+   allow a degree seven polynomial.  (Note: The zeroth word of state
+   information also has some other information stored in it; see setstate
+   for details).  The random number generation technique is a linear feedback
+   shift register approach, employing trinomials (since there are fewer terms
+   to sum up that way).  In this approach, the least significant bit of all
+   the numbers in the state table will act as a linear feedback shift register,
+   and will have period 2^deg - 1 (where deg is the degree of the polynomial
+   being used, assuming that the polynomial is irreducible and primitive).
+   The higher order bits will have longer periods, since their values are
+   also influenced by pseudo-random carries out of the lower bits.  The
+   total period of the generator is approximately deg*(2**deg - 1); thus
+   doubling the amount of state information has a vast influence on the
+   period of the generator.  Note: The deg*(2**deg - 1) is an approximation
+   only good for large deg, when the period of the shift register is the
+   dominant factor.  With deg equal to seven, the period is actually much
+   longer than the 7*(2**7 - 1) predicted by this formula.  */
+
+
+
+/* For each of the currently supported random number generators, we have a
+   break value on the amount of state information (you need at least this many
+   bytes of state info to support this random number generator), a degree for
+   the polynomial (actually a trinomial) that the R.N.G. is based on, and
+   separation between the two lower order coefficients of the trinomial.  */
+
+/* Linear congruential.  */
+#define	TYPE_0		0
+#define	BREAK_0		8
+#define	DEG_0		0
+#define	SEP_0		0
+
+/* x**7 + x**3 + 1.  */
+#define	TYPE_1		1
+#define	BREAK_1		32
+#define	DEG_1		7
+#define	SEP_1		3
 
-#define CRANK(a,b,c,m,s) 	\
-	q = s/a;		\
-	s = b*(s-a*q) - c*q;	\
-	if(s<0) s+=m;
+/* x**15 + x + 1.  */
+#define	TYPE_2		2
+#define	BREAK_2		64
+#define	DEG_2		15
+#define	SEP_2		1
 
-long int random()
+/* x**31 + x**3 + 1.  */
+#define	TYPE_3		3
+#define	BREAK_3		128
+#define	DEG_3		31
+#define	SEP_3		3
+
+/* x**63 + x + 1.  */
+#define	TYPE_4		4
+#define	BREAK_4		256
+#define	DEG_4		63
+#define	SEP_4		1
+
+
+/* Array versions of the above information to make code run faster.
+   Relies on fact that TYPE_i == i.  */
+
+#define	MAX_TYPES	5	/* Max number of types above.  */
+
+
+/* Initially, everything is set up as if from:
+	initstate(1, randtbl, 128);
+   Note that this initialization takes advantage of the fact that srandom
+   advances the front and rear pointers 10*rand_deg times, and hence the
+   rear pointer which starts at 0 will also end up at zero; thus the zeroth
+   element of the state information, which contains info about the current
+   position of the rear pointer is just
+	(MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3.  */
+
+static int32_t randtbl[DEG_3 + 1] =
 {
-	register long int q;
+    TYPE_3,
 
-	CRANK(206, 157, 31, 32363, seed1);
-	CRANK(217, 146, 45, 31727, seed2);
-	CRANK(222, 142, 133, 31657, seed3);
+    -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
+    1627687941, -179304937, -2073333483, 1780058412, -1989503057,
+    -615974602, 344556628, 939512070, -1249116260, 1507946756,
+    -812545463, 154635395, 1388815473, -1926676823, 525320961,
+    -1009028674, 968117788, -123449607, 1284210865, 435012392,
+    -2017506339, -911064859, -370259173, 1132637927, 1398500161,
+    -205601318,
+};
 
-	return seed1 ^ seed2 ^ seed3;
+
+static struct random_data unsafe_state =
+{
+    /* FPTR and RPTR are two pointers into the state info, a front and a rear
+       pointer.  These two pointers are always rand_sep places aparts, as they
+       cycle through the state information.  (Yes, this does mean we could get
+       away with just one pointer, but the code for random is more efficient
+       this way).  The pointers are left positioned as they would be from the call:
+       initstate(1, randtbl, 128);
+       (The position of the rear pointer, rptr, is really 0 (as explained above
+       in the initialization of randtbl) because the state table pointer is set
+       to point to randtbl[1] (as explained below).)  */
+
+    fptr : &randtbl[SEP_3 + 1],
+    rptr : &randtbl[1],
+
+    /* The following things are the pointer to the state information table,
+       the type of the current generator, the degree of the current polynomial
+       being used, and the separation between the two pointers.
+       Note that for efficiency of random, we remember the first location of
+       the state information, not the zeroth.  Hence it is valid to access
+       state[-1], which is used to store the type of the R.N.G.
+       Also, we remember the last location, since this is more efficient than
+       indexing every time to find the address of the last element to see if
+       the front and rear pointers have wrapped.  */
+
+    state : &randtbl[1],
+
+    rand_type : TYPE_3,
+    rand_deg : DEG_3,
+    rand_sep : SEP_3,
+
+    end_ptr : &randtbl[sizeof (randtbl) / sizeof (randtbl[0])]
+};
+
+
+/* Initialize the random number generator based on the given seed.  If the
+   type is the trivial no-state-information type, just remember the seed.
+   Otherwise, initializes state[] based on the given "seed" via a linear
+   congruential generator.  Then, the pointers are set to known locations
+   that are exactly rand_sep places apart.  Lastly, it cycles the state
+   information a given number of times to get rid of any initial dependencies
+   introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
+   for default usage relies on values produced by this routine.  */
+void srandom (unsigned int x)
+{
+    pthread_mutex_lock(&lock);
+    srandom_r (x, &unsafe_state);
+    pthread_mutex_unlock(&lock);
+}
+weak_alias (srandom, srand)
+
+/* Initialize the state information in the given array of N bytes for
+   future random number generation.  Based on the number of bytes we
+   are given, and the break values for the different R.N.G.'s, we choose
+   the best (largest) one we can and set things up for it.  srandom is
+   then called to initialize the state information.  Note that on return
+   from srandom, we set state[-1] to be the type multiplexed with the current
+   value of the rear pointer; this is so successive calls to initstate won't
+   lose this information and will be able to restart with setstate.
+   Note: The first thing we do is save the current state, if any, just like
+   setstate so that it doesn't matter when initstate is called.
+   Returns a pointer to the old state.  */
+char * initstate (unsigned int seed, char *arg_state, size_t n)
+{
+    int32_t *ostate;
+
+    pthread_mutex_lock(&lock);
+    ostate = &unsafe_state.state[-1];
+    initstate_r (seed, arg_state, n, &unsafe_state);
+    pthread_mutex_unlock(&lock);
+    return (char *) ostate;
 }
 
-void srandom(unsigned int seed)
+/* Restore the state from the given state array.
+   Note: It is important that we also remember the locations of the pointers
+   in the current state information, and restore the locations of the pointers
+   from the old state information.  This is done by multiplexing the pointer
+   location into the zeroth word of the state information. Note that due
+   to the order in which things are done, it is OK to call setstate with the
+   same state as the current state
+   Returns a pointer to the old state information.  */
+char * setstate (char *arg_state)
 {
-	seed &= RAND_MAX;
-	seed1 = seed % 32362 + 1;
-	seed2 = seed % 31726 + 1;
-	seed3 = seed % 31656 + 1;
+    int32_t *ostate;
+
+    pthread_mutex_lock(&lock);
+    ostate = &unsafe_state.state[-1];
+    if (setstate_r (arg_state, &unsafe_state) < 0)
+	ostate = NULL;
+    pthread_mutex_unlock(&lock);
+    return (char *) ostate;
+}
+
+/* If we are using the trivial TYPE_0 R.N.G., just do the old linear
+   congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
+   same in all the other cases due to all the global variables that have been
+   set up.  The basic operation is to add the number at the rear pointer into
+   the one at the front pointer.  Then both pointers are advanced to the next
+   location cyclically in the table.  The value returned is the sum generated,
+   reduced to 31 bits by throwing away the "least random" low bit.
+   Note: The code takes advantage of the fact that both the front and
+   rear pointers can't wrap on the same call by not testing the rear
+   pointer if the front one has wrapped.  Returns a 31-bit random number.  */
+
+long int random ()
+{
+  int32_t retval;
+
+  pthread_mutex_lock(&lock);
+  random_r (&unsafe_state, &retval);
+  pthread_mutex_unlock(&lock);
+  return retval;
 }
 
-weak_alias(srandom, srand);
diff --git a/libc/stdlib/random_r.c b/libc/stdlib/random_r.c
new file mode 100644
index 000000000..fce3a98ab
--- /dev/null
+++ b/libc/stdlib/random_r.c
@@ -0,0 +1,365 @@
+/*
+ * Copyright (c) 1983 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that the above copyright notice and this paragraph are
+ * duplicated in all such forms and that any documentation,
+ * advertising materials, and other materials related to such
+ * distribution and use acknowledge that the software was developed
+ * by the University of California, Berkeley.  The name of the
+ * University may not be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+/*
+ * This is derived from the Berkeley source:
+ *	@(#)random.c	5.5 (Berkeley) 7/6/88
+ * It was reworked for the GNU C Library by Roland McGrath.
+ * Rewritten to be reentrant by Ulrich Drepper, 1995
+ */
+
+#define _GNU_SOURCE
+#include <features.h>
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+
+
+/* An improved random number generation package.  In addition to the standard
+   rand()/srand() like interface, this package also has a special state info
+   interface.  The initstate() routine is called with a seed, an array of
+   bytes, and a count of how many bytes are being passed in; this array is
+   then initialized to contain information for random number generation with
+   that much state information.  Good sizes for the amount of state
+   information are 32, 64, 128, and 256 bytes.  The state can be switched by
+   calling the setstate() function with the same array as was initialized
+   with initstate().  By default, the package runs with 128 bytes of state
+   information and generates far better random numbers than a linear
+   congruential generator.  If the amount of state information is less than
+   32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
+   state information is treated as an array of longs; the zeroth element of
+   the array is the type of R.N.G. being used (small integer); the remainder
+   of the array is the state information for the R.N.G.  Thus, 32 bytes of
+   state information will give 7 longs worth of state information, which will
+   allow a degree seven polynomial.  (Note: The zeroth word of state
+   information also has some other information stored in it; see setstate
+   for details).  The random number generation technique is a linear feedback
+   shift register approach, employing trinomials (since there are fewer terms
+   to sum up that way).  In this approach, the least significant bit of all
+   the numbers in the state table will act as a linear feedback shift register,
+   and will have period 2^deg - 1 (where deg is the degree of the polynomial
+   being used, assuming that the polynomial is irreducible and primitive).
+   The higher order bits will have longer periods, since their values are
+   also influenced by pseudo-random carries out of the lower bits.  The
+   total period of the generator is approximately deg*(2**deg - 1); thus
+   doubling the amount of state information has a vast influence on the
+   period of the generator.  Note: The deg*(2**deg - 1) is an approximation
+   only good for large deg, when the period of the shift register is the
+   dominant factor.  With deg equal to seven, the period is actually much
+   longer than the 7*(2**7 - 1) predicted by this formula.  */
+
+
+
+/* For each of the currently supported random number generators, we have a
+   break value on the amount of state information (you need at least this many
+   bytes of state info to support this random number generator), a degree for
+   the polynomial (actually a trinomial) that the R.N.G. is based on, and
+   separation between the two lower order coefficients of the trinomial.  */
+
+/* Linear congruential.  */
+#define	TYPE_0		0
+#define	BREAK_0		8
+#define	DEG_0		0
+#define	SEP_0		0
+
+/* x**7 + x**3 + 1.  */
+#define	TYPE_1		1
+#define	BREAK_1		32
+#define	DEG_1		7
+#define	SEP_1		3
+
+/* x**15 + x + 1.  */
+#define	TYPE_2		2
+#define	BREAK_2		64
+#define	DEG_2		15
+#define	SEP_2		1
+
+/* x**31 + x**3 + 1.  */
+#define	TYPE_3		3
+#define	BREAK_3		128
+#define	DEG_3		31
+#define	SEP_3		3
+
+/* x**63 + x + 1.  */
+#define	TYPE_4		4
+#define	BREAK_4		256
+#define	DEG_4		63
+#define	SEP_4		1
+
+
+/* Array versions of the above information to make code run faster.
+   Relies on fact that TYPE_i == i.  */
+
+#define	MAX_TYPES	5	/* Max number of types above.  */
+
+struct random_poly_info
+{
+    int seps[MAX_TYPES];
+    int degrees[MAX_TYPES];
+};
+
+static const struct random_poly_info random_poly_info =
+{
+    { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
+    { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
+};
+
+
+
+
+/* Initialize the random number generator based on the given seed.  If the
+   type is the trivial no-state-information type, just remember the seed.
+   Otherwise, initializes state[] based on the given "seed" via a linear
+   congruential generator.  Then, the pointers are set to known locations
+   that are exactly rand_sep places apart.  Lastly, it cycles the state
+   information a given number of times to get rid of any initial dependencies
+   introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
+   for default usage relies on values produced by this routine.  */
+int srandom_r (unsigned int seed, struct random_data *buf)
+{
+    int type;
+    int32_t *state;
+    long int i;
+    long int word;
+    int32_t *dst;
+    int kc;
+
+    if (buf == NULL)
+	goto fail;
+    type = buf->rand_type;
+    if ((unsigned int) type >= MAX_TYPES)
+	goto fail;
+
+    state = buf->state;
+    /* We must make sure the seed is not 0.  Take arbitrarily 1 in this case.  */
+    if (seed == 0)
+	seed = 1;
+    state[0] = seed;
+    if (type == TYPE_0)
+	goto done;
+
+    dst = state;
+    word = seed;
+    kc = buf->rand_deg;
+    for (i = 1; i < kc; ++i)
+    {
+	/* This does:
+	   state[i] = (16807 * state[i - 1]) % 2147483647;
+	   but avoids overflowing 31 bits.  */
+	long int hi = word / 127773;
+	long int lo = word % 127773;
+	word = 16807 * lo - 2836 * hi;
+	if (word < 0)
+	    word += 2147483647;
+	*++dst = word;
+    }
+
+    buf->fptr = &state[buf->rand_sep];
+    buf->rptr = &state[0];
+    kc *= 10;
+    while (--kc >= 0)
+    {
+	int32_t discard;
+	(void) random_r (buf, &discard);
+    }
+
+done:
+    return 0;
+
+fail:
+    return -1;
+}
+
+/* Initialize the state information in the given array of N bytes for
+   future random number generation.  Based on the number of bytes we
+   are given, and the break values for the different R.N.G.'s, we choose
+   the best (largest) one we can and set things up for it.  srandom is
+   then called to initialize the state information.  Note that on return
+   from srandom, we set state[-1] to be the type multiplexed with the current
+   value of the rear pointer; this is so successive calls to initstate won't
+   lose this information and will be able to restart with setstate.
+   Note: The first thing we do is save the current state, if any, just like
+   setstate so that it doesn't matter when initstate is called.
+   Returns a pointer to the old state.  */
+int initstate_r (seed, arg_state, n, buf)
+     unsigned int seed;
+     char *arg_state;
+     size_t n;
+     struct random_data *buf;
+{
+    int type;
+    int degree;
+    int separation;
+    int32_t *state;
+
+    if (buf == NULL)
+	goto fail;
+
+    if (n >= BREAK_3)
+	type = n < BREAK_4 ? TYPE_3 : TYPE_4;
+    else if (n < BREAK_1)
+    {
+	if (n < BREAK_0)
+	{
+	    __set_errno (EINVAL);
+	    goto fail;
+	}
+	type = TYPE_0;
+    }
+    else
+	type = n < BREAK_2 ? TYPE_1 : TYPE_2;
+
+    degree = random_poly_info.degrees[type];
+    separation = random_poly_info.seps[type];
+
+    buf->rand_type = type;
+    buf->rand_sep = separation;
+    buf->rand_deg = degree;
+    state = &((int32_t *) arg_state)[1];	/* First location.  */
+    /* Must set END_PTR before srandom.  */
+    buf->end_ptr = &state[degree];
+
+    buf->state = state;
+
+    srandom_r (seed, buf);
+
+    state[-1] = TYPE_0;
+    if (type != TYPE_0)
+	state[-1] = (buf->rptr - state) * MAX_TYPES + type;
+
+    return 0;
+
+fail:
+    __set_errno (EINVAL);
+    return -1;
+}
+
+/* Restore the state from the given state array.
+   Note: It is important that we also remember the locations of the pointers
+   in the current state information, and restore the locations of the pointers
+   from the old state information.  This is done by multiplexing the pointer
+   location into the zeroth word of the state information. Note that due
+   to the order in which things are done, it is OK to call setstate with the
+   same state as the current state
+   Returns a pointer to the old state information.  */
+int setstate_r (char *arg_state, struct random_data *buf)
+{
+    int32_t *new_state = 1 + (int32_t *) arg_state;
+    int type;
+    int old_type;
+    int32_t *old_state;
+    int degree;
+    int separation;
+
+    if (arg_state == NULL || buf == NULL)
+	goto fail;
+
+    old_type = buf->rand_type;
+    old_state = buf->state;
+    if (old_type == TYPE_0)
+	old_state[-1] = TYPE_0;
+    else
+	old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
+
+    type = new_state[-1] % MAX_TYPES;
+    if (type < TYPE_0 || type > TYPE_4)
+	goto fail;
+
+    buf->rand_deg = degree = random_poly_info.degrees[type];
+    buf->rand_sep = separation = random_poly_info.seps[type];
+    buf->rand_type = type;
+
+    if (type != TYPE_0)
+    {
+	int rear = new_state[-1] / MAX_TYPES;
+	buf->rptr = &new_state[rear];
+	buf->fptr = &new_state[(rear + separation) % degree];
+    }
+    buf->state = new_state;
+    /* Set end_ptr too.  */
+    buf->end_ptr = &new_state[degree];
+
+    return 0;
+
+fail:
+    __set_errno (EINVAL);
+    return -1;
+}
+
+/* If we are using the trivial TYPE_0 R.N.G., just do the old linear
+   congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
+   same in all the other cases due to all the global variables that have been
+   set up.  The basic operation is to add the number at the rear pointer into
+   the one at the front pointer.  Then both pointers are advanced to the next
+   location cyclically in the table.  The value returned is the sum generated,
+   reduced to 31 bits by throwing away the "least random" low bit.
+   Note: The code takes advantage of the fact that both the front and
+   rear pointers can't wrap on the same call by not testing the rear
+   pointer if the front one has wrapped.  Returns a 31-bit random number.  */
+
+int random_r (buf, result)
+     struct random_data *buf;
+     int32_t *result;
+{
+    int32_t *state;
+
+    if (buf == NULL || result == NULL)
+	goto fail;
+
+    state = buf->state;
+
+    if (buf->rand_type == TYPE_0)
+    {
+	int32_t val = state[0];
+	val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
+	state[0] = val;
+	*result = val;
+    }
+    else
+    {
+	int32_t *fptr = buf->fptr;
+	int32_t *rptr = buf->rptr;
+	int32_t *end_ptr = buf->end_ptr;
+	int32_t val;
+
+	val = *fptr += *rptr;
+	/* Chucking least random bit.  */
+	*result = (val >> 1) & 0x7fffffff;
+	++fptr;
+	if (fptr >= end_ptr)
+	{
+	    fptr = state;
+	    ++rptr;
+	}
+	else
+	{
+	    ++rptr;
+	    if (rptr >= end_ptr)
+		rptr = state;
+	}
+	buf->fptr = fptr;
+	buf->rptr = rptr;
+    }
+    return 0;
+
+fail:
+    __set_errno (EINVAL);
+    return -1;
+}
+