Prime numbers are interesting for testing components that use multiplies and divides, such as testing DRM's struct drm_mm alignment computations.
v2: Move to lib/, add selftest v3: Fix initial constants (exclude 0/1 from being primes) v4: More RCU markup to keep 0day/sparse happy
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Lukas Wunner lukas@wunner.de --- include/linux/prime_numbers.h | 13 +++ lib/Kconfig | 7 ++ lib/Makefile | 2 + lib/prime_numbers.c | 238 ++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 260 insertions(+) create mode 100644 include/linux/prime_numbers.h create mode 100644 lib/prime_numbers.c
diff --git a/include/linux/prime_numbers.h b/include/linux/prime_numbers.h new file mode 100644 index 000000000000..877f6acbd0b6 --- /dev/null +++ b/include/linux/prime_numbers.h @@ -0,0 +1,13 @@ +#ifndef __LINUX_PRIME_NUMBERS_H +#define __LINUX_PRIME_NUMBERS_H + +#include <linux/types.h> + +bool is_prime_number(unsigned long x); +unsigned long next_prime_number(unsigned long x); + +/* A useful white-lie here is that 1 is prime. */ +#define for_each_prime_number(prime, max) \ + for (prime = 1; prime < (max); prime = next_prime_number(prime)) + +#endif /* !__LINUX_PRIME_NUMBERS_H */ diff --git a/lib/Kconfig b/lib/Kconfig index 260a80e313b9..1788a1f50d28 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -550,4 +550,11 @@ config STACKDEPOT config SBITMAP bool
+config PRIME_NUMBERS + tristate "Prime number generator" + default n + help + Provides a helper module to generate prime numbers. Useful for writing + test code, especially when checking multiplication and divison. + endmenu diff --git a/lib/Makefile b/lib/Makefile index 50144a3aeebd..c664143fd917 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -197,6 +197,8 @@ obj-$(CONFIG_ASN1) += asn1_decoder.o
obj-$(CONFIG_FONT_SUPPORT) += fonts/
+obj-$(CONFIG_PRIME_NUMBERS) += prime_numbers.o + hostprogs-y := gen_crc32table clean-files := crc32table.h
diff --git a/lib/prime_numbers.c b/lib/prime_numbers.c new file mode 100644 index 000000000000..ec2959520653 --- /dev/null +++ b/lib/prime_numbers.c @@ -0,0 +1,238 @@ +#define pr_fmt(fmt) "prime numbers: " fmt "\n" + +#include <linux/module.h> +#include <linux/mutex.h> +#include <linux/prime_numbers.h> +#include <linux/slab.h> + +struct primes { + struct rcu_head rcu; + unsigned long last, sz; + unsigned long primes[]; +}; + +#if BITS_PER_LONG == 64 +static const struct primes small_primes = { + .last = 61, + .sz = 64, + .primes = { 0x28208a20a08a28acUL } +}; +#elif BITS_PER_LONG == 32 +static const struct primes small_primes = { + .last = 31, + .sz = 32, + .primes = { 0xa08a28acUL } +}; +#else +#error "unhandled BITS_PER_LONG" +#endif + +static DEFINE_MUTEX(lock); +static const struct primes __rcu *primes = RCU_INITIALIZER(&small_primes); + +static unsigned long selftest_max; + +static bool slow_is_prime_number(unsigned long x) +{ + unsigned long y = int_sqrt(x); + + while (y > 1) { + if ((x % y) == 0) + break; + y--; + } + + return y == 1; +} + +static unsigned long slow_next_prime_number(unsigned long x) +{ + for (;;) { + if (slow_is_prime_number(++x)) + return x; + } +} + +static unsigned long mark_multiples(unsigned long x, + unsigned long *p, + unsigned long start, + unsigned long end) +{ + unsigned long m; + + m = 2 * x; + if (m < start) + m = roundup(start, x); + + while (m < end) { + __clear_bit(m, p); + m += x; + } + + return x; +} + +static const struct primes *expand_to_next(unsigned long x) +{ + const struct primes *p; + struct primes *new; + unsigned long sz, y; + + rcu_read_unlock(); + + /* Betrand's Theorem states: + * For all n > 1, there exists a prime p: n < p <= 2*n. + */ + sz = 2 * x + 1; + if (sz < x) + return NULL; + + sz = round_up(sz, BITS_PER_LONG); + new = kmalloc(sizeof(*new) + sz / sizeof(long), GFP_KERNEL); + if (!new) + return NULL; + + mutex_lock(&lock); + p = rcu_dereference_protected(primes, lockdep_is_held(&lock)); + if (x < p->last) { + kfree(new); + goto relock; + } + + /* Where memory permits, track the primes using the + * Sieve of Eratosthenes. + */ + memcpy(new->primes, p->primes, p->sz / BITS_PER_LONG * sizeof(long)); + memset(new->primes + p->sz / BITS_PER_LONG, + 0xff, (sz - p->sz) / BITS_PER_LONG * sizeof(long)); + for (y = 2UL; y < sz; y = find_next_bit(new->primes, sz, y + 1)) + new->last = mark_multiples(y, new->primes, p->sz, sz); + new->sz = sz; + + rcu_assign_pointer(primes, new); + if (p != &small_primes) + kfree_rcu((struct primes *)p, rcu); + p = new; + +relock: + rcu_read_lock(); + mutex_unlock(&lock); + return p; +} + +static const struct primes *get_primes(unsigned long x) +{ + const struct primes *p; + + rcu_read_lock(); + p = rcu_dereference(primes); + if (!p || x >= p->last) + p = expand_to_next(x); + + /* returns under RCU iff p != NULL */ + return p; +} + +unsigned long next_prime_number(unsigned long x) +{ + const struct primes *p; + + p = get_primes(x); + if (unlikely(!p)) + return slow_next_prime_number(x); + + x = find_next_bit(p->primes, p->last, x + 1); + rcu_read_unlock(); + + return x; +} +EXPORT_SYMBOL(next_prime_number); + +bool is_prime_number(unsigned long x) +{ + const struct primes *p; + bool result; + + p = get_primes(x); + if (unlikely(!p)) + return slow_is_prime_number(x); + + result = test_bit(x, p->primes); + rcu_read_unlock(); + + return result; +} +EXPORT_SYMBOL(is_prime_number); + +static void dump_primes(void) +{ + const struct primes *p; + + rcu_read_lock(); + p = rcu_dereference(primes); + pr_info("primes.{last=%lu, .sz=%lu, .primes[]=...x%lx}", + p->last, p->sz, p->primes[p->sz / BITS_PER_LONG - 1]); + rcu_read_unlock(); +} + +static int selftest(unsigned long max) +{ + unsigned long x, last; + + if (!max) + return 0; + + for (last = 0, x = 2; x < max; x++) { + bool slow = slow_is_prime_number(x); + bool fast = is_prime_number(x); + + if (slow != fast) { + pr_err("inconsistent result for is-prime(%lu): slow=%s, fast=%s!", + x, slow ? "yes" : "no", fast ? "yes" : "no"); + goto err; + } + + if (!slow) + continue; + + if (next_prime_number(last) != x) { + pr_err("incorrect result for next-prime(%lu): expected %lu, got %lu", + last, x, next_prime_number(last)); + goto err; + } + last = x; + } + + pr_info("selftest(%lu) passed, last prime was %lu", x, last); + return 0; + +err: + dump_primes(); + return -EINVAL; +} + +static int __init primes_init(void) +{ + return selftest(selftest_max); +} + +static void __exit primes_exit(void) +{ + const struct primes *p; + + mutex_lock(&lock); + p = rcu_dereference_protected(primes, lockdep_is_held(&lock)); + if (p != &small_primes) { + kfree_rcu((struct primes *)p, rcu); + rcu_assign_pointer(p, &small_primes); + } + mutex_unlock(&lock); +} + +module_init(primes_init); +module_exit(primes_exit); + +module_param_named(selftest, selftest_max, ulong, 0400); + +MODULE_AUTHOR("Intel Corporation"); +MODULE_LICENSE("GPL");