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mul_u64_u64_div_u64: basic sanity test

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Verify that edge cases produce proper results, and some more.

[npitre@baylibre.com: avoid undefined shift value]
  Link: https://lkml.kernel.org/r/7rrs9pn1-n266-3013-9q6n-1osp8r8s0rrn@syhkavp.arg
Link: https://lkml.kernel.org/r/20240707190648.1982714-3-nico@fluxnic.net
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Cc: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Nicolas Pitre 2024-07-07 15:05:20 -04:00 committed by Andrew Morton
parent b29a62d87c
commit 1635e62e75
4 changed files with 118 additions and 1 deletions
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10
lib/Kconfig.debug
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@ -2280,6 +2280,16 @@ config TEST_DIV64
If unsure, say N.
config TEST_MULDIV64
tristate "mul_u64_u64_div_u64() test"
depends on DEBUG_KERNEL || m
help
Enable this to turn on 'mul_u64_u64_div_u64()' function test.
This test is executed only once during system boot (so affects
only boot time), or at module load time.
If unsure, say N.
config TEST_IOV_ITER
tristate "Test iov_iter operation" if !KUNIT_ALL_TESTS
depends on KUNIT

1
lib/math/Makefile
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@ -6,4 +6,5 @@ obj-$(CONFIG_PRIME_NUMBERS) += prime_numbers.o
obj-$(CONFIG_RATIONAL) += rational.o
obj-$(CONFIG_TEST_DIV64) += test_div64.o
obj-$(CONFIG_TEST_MULDIV64) += test_mul_u64_u64_div_u64.o
obj-$(CONFIG_RATIONAL_KUNIT_TEST) += rational-test.o

9
lib/math/div64.c
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@ -212,11 +212,18 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
#endif
/* make sure c is not zero, trigger exception otherwise */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdiv-by-zero"
if (unlikely(c == 0))
return 1/0;
#pragma GCC diagnostic pop
int shift = __builtin_ctzll(c);
/* try reducing the fraction in case the dividend becomes <= 64 bits */
if ((n_hi >> shift) == 0) {
u64 n = (n_lo >> shift) | (n_hi << (64 - shift));
u64 n = shift ? (n_lo >> shift) | (n_hi << (64 - shift)) : n_lo;
return div64_u64(n, c >> shift);
/*

99
lib/math/test_mul_u64_u64_div_u64.c Normal file
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@ -0,0 +1,99 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2024 BayLibre SAS
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/init.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/math64.h>
typedef struct { u64 a; u64 b; u64 c; u64 result; } test_params;
static test_params test_values[] = {
/* this contains many edge values followed by a couple random values */
{ 0xb, 0x7, 0x3, 0x19 },
{ 0xffff0000, 0xffff0000, 0xf, 0x1110eeef00000000 },
{ 0xffffffff, 0xffffffff, 0x1, 0xfffffffe00000001 },
{ 0xffffffff, 0xffffffff, 0x2, 0x7fffffff00000000 },
{ 0x1ffffffff, 0xffffffff, 0x2, 0xfffffffe80000000 },
{ 0x1ffffffff, 0xffffffff, 0x3, 0xaaaaaaa9aaaaaaab },
{ 0x1ffffffff, 0x1ffffffff, 0x4, 0xffffffff00000000 },
{ 0xffff000000000000, 0xffff000000000000, 0xffff000000000001, 0xfffeffffffffffff },
{ 0x3333333333333333, 0x3333333333333333, 0x5555555555555555, 0x1eb851eb851eb851 },
{ 0x7fffffffffffffff, 0x2, 0x3, 0x5555555555555554 },
{ 0xffffffffffffffff, 0x2, 0x8000000000000000, 0x3 },
{ 0xffffffffffffffff, 0x2, 0xc000000000000000, 0x2 },
{ 0xffffffffffffffff, 0x4000000000000004, 0x8000000000000000, 0x8000000000000007 },
{ 0xffffffffffffffff, 0x4000000000000001, 0x8000000000000000, 0x8000000000000001 },
{ 0xffffffffffffffff, 0x8000000000000001, 0xffffffffffffffff, 0x8000000000000001 },
{ 0xfffffffffffffffe, 0x8000000000000001, 0xffffffffffffffff, 0x8000000000000000 },
{ 0xffffffffffffffff, 0x8000000000000001, 0xfffffffffffffffe, 0x8000000000000001 },
{ 0xffffffffffffffff, 0x8000000000000001, 0xfffffffffffffffd, 0x8000000000000002 },
{ 0x7fffffffffffffff, 0xffffffffffffffff, 0xc000000000000000, 0xaaaaaaaaaaaaaaa8 },
{ 0xffffffffffffffff, 0x7fffffffffffffff, 0xa000000000000000, 0xccccccccccccccca },
{ 0xffffffffffffffff, 0x7fffffffffffffff, 0x9000000000000000, 0xe38e38e38e38e38b },
{ 0x7fffffffffffffff, 0x7fffffffffffffff, 0x5000000000000000, 0xccccccccccccccc9 },
{ 0xffffffffffffffff, 0xfffffffffffffffe, 0xffffffffffffffff, 0xfffffffffffffffe },
{ 0xe6102d256d7ea3ae, 0x70a77d0be4c31201, 0xd63ec35ab3220357, 0x78f8bf8cc86c6e18 },
{ 0xf53bae05cb86c6e1, 0x3847b32d2f8d32e0, 0xcfd4f55a647f403c, 0x42687f79d8998d35 },
{ 0x9951c5498f941092, 0x1f8c8bfdf287a251, 0xa3c8dc5f81ea3fe2, 0x1d887cb25900091f },
{ 0x374fee9daa1bb2bb, 0x0d0bfbff7b8ae3ef, 0xc169337bd42d5179, 0x03bb2dbaffcbb961 },
{ 0xeac0d03ac10eeaf0, 0x89be05dfa162ed9b, 0x92bb1679a41f0e4b, 0xdc5f5cc9e270d216 },
};
/*
* The above table can be verified with the following shell script:
*
* #!/bin/sh
* sed -ne 's/^{ \+\(.*\), \+\(.*\), \+\(.*\), \+\(.*\) },$/\1 \2 \3 \4/p' \
* lib/math/test_mul_u64_u64_div_u64.c |
* while read a b c r; do
* expected=$( printf "obase=16; ibase=16; %X * %X / %X\n" $a $b $c | bc )
* given=$( printf "%X\n" $r )
* if [ "$expected" = "$given" ]; then
* echo "$a * $b / $c = $r OK"
* else
* echo "$a * $b / $c = $r is wrong" >&2
* echo "should be equivalent to 0x$expected" >&2
* exit 1
* fi
* done
*/
static int __init test_init(void)
{
int i;
pr_info("Starting mul_u64_u64_div_u64() test\n");
for (i = 0; i < ARRAY_SIZE(test_values); i++) {
u64 a = test_values[i].a;
u64 b = test_values[i].b;
u64 c = test_values[i].c;
u64 expected_result = test_values[i].result;
u64 result = mul_u64_u64_div_u64(a, b, c);
if (result != expected_result) {
pr_err("ERROR: 0x%016llx * 0x%016llx / 0x%016llx\n", a, b, c);
pr_err("ERROR: expected result: %016llx\n", expected_result);
pr_err("ERROR: obtained result: %016llx\n", result);
}
}
pr_info("Completed mul_u64_u64_div_u64() test\n");
return 0;
}
static void __exit test_exit(void)
{
}
module_init(test_init);
module_exit(test_exit);
MODULE_AUTHOR("Nicolas Pitre");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("mul_u64_u64_div_u64() test module");