2 * Non-physical true random number generator based on timing jitter --
3 * Jitter RNG standalone code.
5 * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2020
10 * See https://www.chronox.de/jent.html
15 * Redistribution and use in source and binary forms, with or without
16 * modification, are permitted provided that the following conditions
18 * 1. Redistributions of source code must retain the above copyright
19 * notice, and the entire permission notice in its entirety,
20 * including the disclaimer of warranties.
21 * 2. Redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution.
24 * 3. The name of the author may not be used to endorse or promote
25 * products derived from this software without specific prior
28 * ALTERNATIVELY, this product may be distributed under the terms of
29 * the GNU General Public License, in which case the provisions of the GPL2 are
30 * required INSTEAD OF the above restrictions. (This clause is
31 * necessary due to a potential bad interaction between the GPL and
32 * the restrictions contained in a BSD-style copyright.)
34 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
35 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
36 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
37 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
38 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
39 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
40 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
41 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
42 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
43 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
44 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
49 * This Jitterentropy RNG is based on the jitterentropy library
50 * version 2.2.0 provided at https://www.chronox.de/jent.html
54 #error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c."
57 typedef unsigned long long __u64
;
58 typedef long long __s64
;
59 typedef unsigned int __u32
;
60 #define NULL ((void *) 0)
62 /* The entropy pool */
64 /* all data values that are vital to maintain the security
65 * of the RNG are marked as SENSITIVE. A user must not
66 * access that information while the RNG executes its loops to
67 * calculate the next random value. */
68 __u64 data
; /* SENSITIVE Actual random number */
69 __u64 old_data
; /* SENSITIVE Previous random number */
70 __u64 prev_time
; /* SENSITIVE Previous time stamp */
71 #define DATA_SIZE_BITS ((sizeof(__u64)) * 8)
72 __u64 last_delta
; /* SENSITIVE stuck test */
73 __s64 last_delta2
; /* SENSITIVE stuck test */
74 unsigned int osr
; /* Oversample rate */
75 #define JENT_MEMORY_BLOCKS 64
76 #define JENT_MEMORY_BLOCKSIZE 32
77 #define JENT_MEMORY_ACCESSLOOPS 128
78 #define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE)
79 unsigned char *mem
; /* Memory access location with size of
80 * memblocks * memblocksize */
81 unsigned int memlocation
; /* Pointer to byte in *mem */
82 unsigned int memblocks
; /* Number of memory blocks in *mem */
83 unsigned int memblocksize
; /* Size of one memory block in bytes */
84 unsigned int memaccessloops
; /* Number of memory accesses per random
87 /* Repetition Count Test */
88 int rct_count
; /* Number of stuck values */
90 /* Adaptive Proportion Test for a significance level of 2^-30 */
91 #define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */
92 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */
93 /* LSB of time stamp to process */
94 #define JENT_APT_LSB 16
95 #define JENT_APT_WORD_MASK (JENT_APT_LSB - 1)
96 unsigned int apt_observations
; /* Number of collected observations */
97 unsigned int apt_count
; /* APT counter */
98 unsigned int apt_base
; /* APT base reference */
99 unsigned int apt_base_set
:1; /* APT base reference set? */
101 unsigned int health_failure
:1; /* Permanent health failure */
104 /* Flags that can be used to initialize the RNG */
105 #define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
106 * entropy, saves MEMORY_SIZE RAM for
107 * entropy collector */
109 /* -- error codes for init function -- */
110 #define JENT_ENOTIME 1 /* Timer service not available */
111 #define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */
112 #define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */
113 #define JENT_EVARVAR 5 /* Timer does not produce variations of
114 * variations (2nd derivation of time is
116 #define JENT_ESTUCK 8 /* Too many stuck results during init. */
117 #define JENT_EHEALTH 9 /* Health test failed during initialization */
118 #define JENT_ERCT 10 /* RCT failed during initialization */
120 #include "jitterentropy.h"
122 /***************************************************************************
123 * Adaptive Proportion Test
125 * This test complies with SP800-90B section 4.4.2.
126 ***************************************************************************/
129 * Reset the APT counter
131 * @ec [in] Reference to entropy collector
133 static void jent_apt_reset(struct rand_data
*ec
, unsigned int delta_masked
)
135 /* Reset APT counter */
137 ec
->apt_base
= delta_masked
;
138 ec
->apt_observations
= 0;
142 * Insert a new entropy event into APT
144 * @ec [in] Reference to entropy collector
145 * @delta_masked [in] Masked time delta to process
147 static void jent_apt_insert(struct rand_data
*ec
, unsigned int delta_masked
)
149 /* Initialize the base reference */
150 if (!ec
->apt_base_set
) {
151 ec
->apt_base
= delta_masked
;
152 ec
->apt_base_set
= 1;
156 if (delta_masked
== ec
->apt_base
) {
159 if (ec
->apt_count
>= JENT_APT_CUTOFF
)
160 ec
->health_failure
= 1;
163 ec
->apt_observations
++;
165 if (ec
->apt_observations
>= JENT_APT_WINDOW_SIZE
)
166 jent_apt_reset(ec
, delta_masked
);
169 /***************************************************************************
170 * Stuck Test and its use as Repetition Count Test
172 * The Jitter RNG uses an enhanced version of the Repetition Count Test
173 * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
174 * back-to-back values, the input to the RCT is the counting of the stuck
175 * values during the generation of one Jitter RNG output block.
177 * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
179 * During the counting operation, the Jitter RNG always calculates the RCT
180 * cut-off value of C. If that value exceeds the allowed cut-off value,
181 * the Jitter RNG output block will be calculated completely but discarded at
182 * the end. The caller of the Jitter RNG is informed with an error code.
183 ***************************************************************************/
186 * Repetition Count Test as defined in SP800-90B section 4.4.1
188 * @ec [in] Reference to entropy collector
189 * @stuck [in] Indicator whether the value is stuck
191 static void jent_rct_insert(struct rand_data
*ec
, int stuck
)
194 * If we have a count less than zero, a previous RCT round identified
195 * a failure. We will not overwrite it.
197 if (ec
->rct_count
< 0)
204 * The cutoff value is based on the following consideration:
205 * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8.
206 * In addition, we require an entropy value H of 1/OSR as this
207 * is the minimum entropy required to provide full entropy.
208 * Note, we collect 64 * OSR deltas for inserting them into
209 * the entropy pool which should then have (close to) 64 bits
212 * Note, ec->rct_count (which equals to value B in the pseudo
213 * code of SP800-90B section 4.4.1) starts with zero. Hence
214 * we need to subtract one from the cutoff value as calculated
215 * following SP800-90B.
217 if ((unsigned int)ec
->rct_count
>= (31 * ec
->osr
)) {
219 ec
->health_failure
= 1;
227 * Is there an RCT health test failure?
229 * @ec [in] Reference to entropy collector
232 * 0 No health test failure
233 * 1 Permanent health test failure
235 static int jent_rct_failure(struct rand_data
*ec
)
237 if (ec
->rct_count
< 0)
242 static inline __u64
jent_delta(__u64 prev
, __u64 next
)
244 #define JENT_UINT64_MAX (__u64)(~((__u64) 0))
245 return (prev
< next
) ? (next
- prev
) :
246 (JENT_UINT64_MAX
- prev
+ 1 + next
);
250 * Stuck test by checking the:
251 * 1st derivative of the jitter measurement (time delta)
252 * 2nd derivative of the jitter measurement (delta of time deltas)
253 * 3rd derivative of the jitter measurement (delta of delta of time deltas)
255 * All values must always be non-zero.
257 * @ec [in] Reference to entropy collector
258 * @current_delta [in] Jitter time delta
261 * 0 jitter measurement not stuck (good bit)
262 * 1 jitter measurement stuck (reject bit)
264 static int jent_stuck(struct rand_data
*ec
, __u64 current_delta
)
266 __u64 delta2
= jent_delta(ec
->last_delta
, current_delta
);
267 __u64 delta3
= jent_delta(ec
->last_delta2
, delta2
);
269 ec
->last_delta
= current_delta
;
270 ec
->last_delta2
= delta2
;
273 * Insert the result of the comparison of two back-to-back time
276 jent_apt_insert(ec
, current_delta
);
278 if (!current_delta
|| !delta2
|| !delta3
) {
279 /* RCT with a stuck bit */
280 jent_rct_insert(ec
, 1);
284 /* RCT with a non-stuck bit */
285 jent_rct_insert(ec
, 0);
291 * Report any health test failures
293 * @ec [in] Reference to entropy collector
296 * 0 No health test failure
297 * 1 Permanent health test failure
299 static int jent_health_failure(struct rand_data
*ec
)
301 /* Test is only enabled in FIPS mode */
302 if (!jent_fips_enabled())
305 return ec
->health_failure
;
308 /***************************************************************************
310 ***************************************************************************/
313 * Update of the loop count used for the next round of
314 * an entropy collection.
317 * @ec entropy collector struct -- may be NULL
318 * @bits is the number of low bits of the timer to consider
319 * @min is the number of bits we shift the timer value to the right at
320 * the end to make sure we have a guaranteed minimum value
322 * @return Newly calculated loop counter
324 static __u64
jent_loop_shuffle(struct rand_data
*ec
,
325 unsigned int bits
, unsigned int min
)
330 unsigned int mask
= (1<<bits
) - 1;
332 jent_get_nstime(&time
);
334 * Mix the current state of the random number into the shuffle
335 * calculation to balance that shuffle a bit more.
340 * We fold the time value as much as possible to ensure that as many
341 * bits of the time stamp are included as possible.
343 for (i
= 0; ((DATA_SIZE_BITS
+ bits
- 1) / bits
) > i
; i
++) {
344 shuffle
^= time
& mask
;
349 * We add a lower boundary value to ensure we have a minimum
352 return (shuffle
+ (1<<min
));
356 * CPU Jitter noise source -- this is the noise source based on the CPU
357 * execution time jitter
359 * This function injects the individual bits of the time value into the
360 * entropy pool using an LFSR.
362 * The code is deliberately inefficient with respect to the bit shifting
363 * and shall stay that way. This function is the root cause why the code
364 * shall be compiled without optimization. This function not only acts as
365 * folding operation, but this function's execution is used to measure
366 * the CPU execution time jitter. Any change to the loop in this function
367 * implies that careful retesting must be done.
369 * @ec [in] entropy collector struct
370 * @time [in] time stamp to be injected
371 * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
372 * number of loops to perform the folding
373 * @stuck [in] Is the time stamp identified as stuck?
378 * @return Number of loops the folding operation is performed
380 static void jent_lfsr_time(struct rand_data
*ec
, __u64 time
, __u64 loop_cnt
,
386 #define MAX_FOLD_LOOP_BIT 4
387 #define MIN_FOLD_LOOP_BIT 0
388 __u64 fold_loop_cnt
=
389 jent_loop_shuffle(ec
, MAX_FOLD_LOOP_BIT
, MIN_FOLD_LOOP_BIT
);
392 * testing purposes -- allow test app to set the counter, not
393 * needed during runtime
396 fold_loop_cnt
= loop_cnt
;
397 for (j
= 0; j
< fold_loop_cnt
; j
++) {
399 for (i
= 1; (DATA_SIZE_BITS
) >= i
; i
++) {
400 __u64 tmp
= time
<< (DATA_SIZE_BITS
- i
);
402 tmp
= tmp
>> (DATA_SIZE_BITS
- 1);
405 * Fibonacci LSFR with polynomial of
406 * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
407 * primitive according to
408 * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
409 * (the shift values are the polynomial values minus one
410 * due to counting bits from 0 to 63). As the current
411 * position is always the LSB, the polynomial only needs
412 * to shift data in from the left without wrap.
414 tmp
^= ((new >> 63) & 1);
415 tmp
^= ((new >> 60) & 1);
416 tmp
^= ((new >> 55) & 1);
417 tmp
^= ((new >> 30) & 1);
418 tmp
^= ((new >> 27) & 1);
419 tmp
^= ((new >> 22) & 1);
426 * If the time stamp is stuck, do not finally insert the value into
427 * the entropy pool. Although this operation should not do any harm
428 * even when the time stamp has no entropy, SP800-90B requires that
429 * any conditioning operation (SP800-90B considers the LFSR to be a
430 * conditioning operation) to have an identical amount of input
431 * data according to section 3.1.5.
438 * Memory Access noise source -- this is a noise source based on variations in
439 * memory access times
441 * This function performs memory accesses which will add to the timing
442 * variations due to an unknown amount of CPU wait states that need to be
443 * added when accessing memory. The memory size should be larger than the L1
444 * caches as outlined in the documentation and the associated testing.
446 * The L1 cache has a very high bandwidth, albeit its access rate is usually
447 * slower than accessing CPU registers. Therefore, L1 accesses only add minimal
448 * variations as the CPU has hardly to wait. Starting with L2, significant
449 * variations are added because L2 typically does not belong to the CPU any more
450 * and therefore a wider range of CPU wait states is necessary for accesses.
451 * L3 and real memory accesses have even a wider range of wait states. However,
452 * to reliably access either L3 or memory, the ec->mem memory must be quite
453 * large which is usually not desirable.
455 * @ec [in] Reference to the entropy collector with the memory access data -- if
456 * the reference to the memory block to be accessed is NULL, this noise
458 * @loop_cnt [in] if a value not equal to 0 is set, use the given value
459 * number of loops to perform the LFSR
461 static void jent_memaccess(struct rand_data
*ec
, __u64 loop_cnt
)
463 unsigned int wrap
= 0;
465 #define MAX_ACC_LOOP_BIT 7
466 #define MIN_ACC_LOOP_BIT 0
468 jent_loop_shuffle(ec
, MAX_ACC_LOOP_BIT
, MIN_ACC_LOOP_BIT
);
470 if (NULL
== ec
|| NULL
== ec
->mem
)
472 wrap
= ec
->memblocksize
* ec
->memblocks
;
475 * testing purposes -- allow test app to set the counter, not
476 * needed during runtime
479 acc_loop_cnt
= loop_cnt
;
481 for (i
= 0; i
< (ec
->memaccessloops
+ acc_loop_cnt
); i
++) {
482 unsigned char *tmpval
= ec
->mem
+ ec
->memlocation
;
484 * memory access: just add 1 to one byte,
485 * wrap at 255 -- memory access implies read
486 * from and write to memory location
488 *tmpval
= (*tmpval
+ 1) & 0xff;
490 * Addition of memblocksize - 1 to pointer
491 * with wrap around logic to ensure that every
492 * memory location is hit evenly
494 ec
->memlocation
= ec
->memlocation
+ ec
->memblocksize
- 1;
495 ec
->memlocation
= ec
->memlocation
% wrap
;
499 /***************************************************************************
500 * Start of entropy processing logic
501 ***************************************************************************/
503 * This is the heart of the entropy generation: calculate time deltas and
504 * use the CPU jitter in the time deltas. The jitter is injected into the
507 * WARNING: ensure that ->prev_time is primed before using the output
508 * of this function! This can be done by calling this function
509 * and not using its result.
511 * @ec [in] Reference to entropy collector
513 * @return result of stuck test
515 static int jent_measure_jitter(struct rand_data
*ec
)
518 __u64 current_delta
= 0;
521 /* Invoke one noise source before time measurement to add variations */
522 jent_memaccess(ec
, 0);
525 * Get time stamp and calculate time delta to previous
526 * invocation to measure the timing variations
528 jent_get_nstime(&time
);
529 current_delta
= jent_delta(ec
->prev_time
, time
);
530 ec
->prev_time
= time
;
532 /* Check whether we have a stuck measurement. */
533 stuck
= jent_stuck(ec
, current_delta
);
535 /* Now call the next noise sources which also injects the data */
536 jent_lfsr_time(ec
, current_delta
, 0, stuck
);
542 * Generator of one 64 bit random number
543 * Function fills rand_data->data
545 * @ec [in] Reference to entropy collector
547 static void jent_gen_entropy(struct rand_data
*ec
)
551 /* priming of the ->prev_time value */
552 jent_measure_jitter(ec
);
555 /* If a stuck measurement is received, repeat measurement */
556 if (jent_measure_jitter(ec
))
560 * We multiply the loop value with ->osr to obtain the
561 * oversampling rate requested by the caller
563 if (++k
>= (DATA_SIZE_BITS
* ec
->osr
))
569 * Entry function: Obtain entropy for the caller.
571 * This function invokes the entropy gathering logic as often to generate
572 * as many bytes as requested by the caller. The entropy gathering logic
573 * creates 64 bit per invocation.
575 * This function truncates the last 64 bit entropy value output to the exact
576 * size specified by the caller.
578 * @ec [in] Reference to entropy collector
579 * @data [in] pointer to buffer for storing random data -- buffer must already
581 * @len [in] size of the buffer, specifying also the requested number of random
584 * @return 0 when request is fulfilled or an error
586 * The following error codes can occur:
587 * -1 entropy_collector is NULL
591 int jent_read_entropy(struct rand_data
*ec
, unsigned char *data
,
594 unsigned char *p
= data
;
602 jent_gen_entropy(ec
);
604 if (jent_health_failure(ec
)) {
607 if (jent_rct_failure(ec
))
613 * Re-initialize the noise source
615 * If the health test fails, the Jitter RNG remains
616 * in failure state and will return a health failure
617 * during next invocation.
619 if (jent_entropy_init())
622 /* Set APT to initial state */
623 jent_apt_reset(ec
, 0);
624 ec
->apt_base_set
= 0;
626 /* Set RCT to initial state */
629 /* Re-enable Jitter RNG */
630 ec
->health_failure
= 0;
633 * Return the health test failure status to the
634 * caller as the generated value is not appropriate.
639 if ((DATA_SIZE_BITS
/ 8) < len
)
640 tocopy
= (DATA_SIZE_BITS
/ 8);
643 jent_memcpy(p
, &ec
->data
, tocopy
);
652 /***************************************************************************
653 * Initialization logic
654 ***************************************************************************/
656 struct rand_data
*jent_entropy_collector_alloc(unsigned int osr
,
659 struct rand_data
*entropy_collector
;
661 entropy_collector
= jent_zalloc(sizeof(struct rand_data
));
662 if (!entropy_collector
)
665 if (!(flags
& JENT_DISABLE_MEMORY_ACCESS
)) {
666 /* Allocate memory for adding variations based on memory
669 entropy_collector
->mem
= jent_zalloc(JENT_MEMORY_SIZE
);
670 if (!entropy_collector
->mem
) {
671 jent_zfree(entropy_collector
);
674 entropy_collector
->memblocksize
= JENT_MEMORY_BLOCKSIZE
;
675 entropy_collector
->memblocks
= JENT_MEMORY_BLOCKS
;
676 entropy_collector
->memaccessloops
= JENT_MEMORY_ACCESSLOOPS
;
679 /* verify and set the oversampling rate */
681 osr
= 1; /* minimum sampling rate is 1 */
682 entropy_collector
->osr
= osr
;
684 /* fill the data pad with non-zero values */
685 jent_gen_entropy(entropy_collector
);
687 return entropy_collector
;
690 void jent_entropy_collector_free(struct rand_data
*entropy_collector
)
692 jent_zfree(entropy_collector
->mem
);
693 entropy_collector
->mem
= NULL
;
694 jent_zfree(entropy_collector
);
697 int jent_entropy_init(void)
702 unsigned int nonstuck
= 0;
703 int time_backwards
= 0;
706 struct rand_data ec
= { 0 };
708 /* Required for RCT */
711 /* We could perform statistical tests here, but the problem is
712 * that we only have a few loop counts to do testing. These
713 * loop counts may show some slight skew and we produce
716 * Moreover, only old systems show potentially problematic
717 * jitter entropy that could potentially be caught here. But
718 * the RNG is intended for hardware that is available or widely
719 * used, but not old systems that are long out of favor. Thus,
720 * no statistical tests.
724 * We could add a check for system capabilities such as clock_getres or
725 * check for CONFIG_X86_TSC, but it does not make much sense as the
726 * following sanity checks verify that we have a high-resolution
730 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
731 * definitely too little.
733 * SP800-90B requires at least 1024 initial test cycles.
735 #define TESTLOOPCOUNT 1024
736 #define CLEARCACHE 100
737 for (i
= 0; (TESTLOOPCOUNT
+ CLEARCACHE
) > i
; i
++) {
741 unsigned int lowdelta
= 0;
744 /* Invoke core entropy collection logic */
745 jent_get_nstime(&time
);
747 jent_lfsr_time(&ec
, time
, 0, 0);
748 jent_get_nstime(&time2
);
750 /* test whether timer works */
753 delta
= jent_delta(time
, time2
);
755 * test whether timer is fine grained enough to provide
756 * delta even when called shortly after each other -- this
757 * implies that we also have a high resolution timer
760 return JENT_ECOARSETIME
;
762 stuck
= jent_stuck(&ec
, delta
);
765 * up to here we did not modify any variable that will be
766 * evaluated later, but we already performed some work. Thus we
767 * already have had an impact on the caches, branch prediction,
768 * etc. with the goal to clear it to get the worst case
780 * Ensure that the APT succeeded.
782 * With the check below that count_stuck must be less
783 * than 10% of the overall generated raw entropy values
784 * it is guaranteed that the APT is invoked at
785 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
787 if ((nonstuck
% JENT_APT_WINDOW_SIZE
) == 0) {
789 delta
& JENT_APT_WORD_MASK
);
790 if (jent_health_failure(&ec
))
796 if (jent_rct_failure(&ec
))
799 /* test whether we have an increasing timer */
803 /* use 32 bit value to ensure compilation on 32 bit arches */
804 lowdelta
= time2
- time
;
805 if (!(lowdelta
% 100))
809 * ensure that we have a varying delta timer which is necessary
810 * for the calculation of entropy -- perform this check
811 * only after the first loop is executed as we need to prime
814 if (delta
> old_delta
)
815 delta_sum
+= (delta
- old_delta
);
817 delta_sum
+= (old_delta
- delta
);
822 * we allow up to three times the time running backwards.
823 * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus,
824 * if such an operation just happens to interfere with our test, it
825 * should not fail. The value of 3 should cover the NTP case being
826 * performed during our test run.
828 if (time_backwards
> 3)
829 return JENT_ENOMONOTONIC
;
832 * Variations of deltas of time must on average be larger
833 * than 1 to ensure the entropy estimation
834 * implied with 1 is preserved
836 if ((delta_sum
) <= 1)
840 * Ensure that we have variations in the time stamp below 10 for at
841 * least 10% of all checks -- on some platforms, the counter increments
842 * in multiples of 100, but not always
844 if ((TESTLOOPCOUNT
/10 * 9) < count_mod
)
845 return JENT_ECOARSETIME
;
848 * If we have more than 90% stuck results, then this Jitter RNG is
849 * likely to not work well.
851 if ((TESTLOOPCOUNT
/10 * 9) < count_stuck
)