// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2021  Maciej W. Rozycki
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/init.h>
#include <linux/ktime.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/time64.h>
#include <linux/types.h>

#include <asm/div64.h>

#define TEST_DIV64_N_ITER 1024

static const u64 test_div64_dividends[] = {
	0x00000000ab275080,
	0x0000000fe73c1959,
	0x000000e54c0a74b1,
	0x00000d4398ff1ef9,
	0x0000a18c2ee1c097,
	0x00079fb80b072e4a,
	0x0072db27380dd689,
	0x0842f488162e2284,
	0xf66745411d8ab063,
};
#define SIZE_DIV64_DIVIDENDS ARRAY_SIZE(test_div64_dividends)

#define TEST_DIV64_DIVISOR_0 0x00000009
#define TEST_DIV64_DIVISOR_1 0x0000007c
#define TEST_DIV64_DIVISOR_2 0x00000204
#define TEST_DIV64_DIVISOR_3 0x0000cb5b
#define TEST_DIV64_DIVISOR_4 0x00010000
#define TEST_DIV64_DIVISOR_5 0x0008a880
#define TEST_DIV64_DIVISOR_6 0x003fd3ae
#define TEST_DIV64_DIVISOR_7 0x0b658fac
#define TEST_DIV64_DIVISOR_8 0xdc08b349

static const u32 test_div64_divisors[] = {
	TEST_DIV64_DIVISOR_0,
	TEST_DIV64_DIVISOR_1,
	TEST_DIV64_DIVISOR_2,
	TEST_DIV64_DIVISOR_3,
	TEST_DIV64_DIVISOR_4,
	TEST_DIV64_DIVISOR_5,
	TEST_DIV64_DIVISOR_6,
	TEST_DIV64_DIVISOR_7,
	TEST_DIV64_DIVISOR_8,
};
#define SIZE_DIV64_DIVISORS ARRAY_SIZE(test_div64_divisors)

static const struct {
	u64 quotient;
	u32 remainder;
} test_div64_results[SIZE_DIV64_DIVISORS][SIZE_DIV64_DIVIDENDS] = {
	{
		{ 0x0000000013045e47, 0x00000001 },
		{ 0x000000000161596c, 0x00000030 },
		{ 0x000000000054e9d4, 0x00000130 },
		{ 0x000000000000d776, 0x0000278e },
		{ 0x000000000000ab27, 0x00005080 },
		{ 0x00000000000013c4, 0x0004ce80 },
		{ 0x00000000000002ae, 0x001e143c },
		{ 0x000000000000000f, 0x0033e56c },
		{ 0x0000000000000000, 0xab275080 },
	}, {
		{ 0x00000001c45c02d1, 0x00000000 },
		{ 0x0000000020d5213c, 0x00000049 },
		{ 0x0000000007e3d65f, 0x000001dd },
		{ 0x0000000000140531, 0x000065ee },
		{ 0x00000000000fe73c, 0x00001959 },
		{ 0x000000000001d637, 0x0004e5d9 },
		{ 0x0000000000003fc9, 0x000713bb },
		{ 0x0000000000000165, 0x029abe7d },
		{ 0x0000000000000012, 0x6e9f7e37 },
	}, {
		{ 0x000000197a3a0cf7, 0x00000002 },
		{ 0x00000001d9632e5c, 0x00000021 },
		{ 0x0000000071c28039, 0x000001cd },
		{ 0x000000000120a844, 0x0000b885 },
		{ 0x0000000000e54c0a, 0x000074b1 },
		{ 0x00000000001a7bb3, 0x00072331 },
		{ 0x00000000000397ad, 0x0002c61b },
		{ 0x000000000000141e, 0x06ea2e89 },
		{ 0x000000000000010a, 0xab002ad7 },
	}, {
		{ 0x0000017949e37538, 0x00000001 },
		{ 0x0000001b62441f37, 0x00000055 },
		{ 0x0000000694a3391d, 0x00000085 },
		{ 0x0000000010b2a5d2, 0x0000a753 },
		{ 0x000000000d4398ff, 0x00001ef9 },
		{ 0x0000000001882ec6, 0x0005cbf9 },
		{ 0x000000000035333b, 0x0017abdf },
		{ 0x00000000000129f1, 0x0ab4520d },
		{ 0x0000000000000f6e, 0x8ac0ce9b },
	}, {
		{ 0x000011f321a74e49, 0x00000006 },
		{ 0x0000014d8481d211, 0x0000005b },
		{ 0x0000005025cbd92d, 0x000001e3 },
		{ 0x00000000cb5e71e3, 0x000043e6 },
		{ 0x00000000a18c2ee1, 0x0000c097 },
		{ 0x0000000012a88828, 0x00036c97 },
		{ 0x000000000287f16f, 0x002c2a25 },
		{ 0x00000000000e2cc7, 0x02d581e3 },
		{ 0x000000000000bbf4, 0x1ba08c03 },
	}, {
		{ 0x0000d8db8f72935d, 0x00000005 },
		{ 0x00000fbd5aed7a2e, 0x00000002 },
		{ 0x000003c84b6ea64a, 0x00000122 },
		{ 0x0000000998fa8829, 0x000044b7 },
		{ 0x000000079fb80b07, 0x00002e4a },
		{ 0x00000000e16b20fa, 0x0002a14a },
		{ 0x000000001e940d22, 0x00353b2e },
		{ 0x0000000000ab40ac, 0x06fba6ba },
		{ 0x000000000008debd, 0x72d98365 },
	}, {
		{ 0x000cc3045b8fc281, 0x00000000 },
		{ 0x0000ed1f48b5c9fc, 0x00000079 },
		{ 0x000038fb9c63406a, 0x000000e1 },
		{ 0x000000909705b825, 0x00000a62 },
		{ 0x00000072db27380d, 0x0000d689 },
		{ 0x0000000d43fce827, 0x00082b09 },
		{ 0x00000001ccaba11a, 0x0037e8dd },
		{ 0x000000000a13f729, 0x0566dffd },
		{ 0x000000000085a14b, 0x23d36726 },
	}, {
		{ 0x00eafeb9c993592b, 0x00000001 },
		{ 0x00110e5befa9a991, 0x00000048 },
		{ 0x00041947b4a1d36a, 0x000000dc },
		{ 0x00000a6679327311, 0x0000c079 },
		{ 0x00000842f488162e, 0x00002284 },
		{ 0x000000f4459740fc, 0x00084484 },
		{ 0x0000002122c47bf9, 0x002ca446 },
		{ 0x00000000b9936290, 0x004979c4 },
		{ 0x00000000099ca89d, 0x9db446bf },
	}, {
		{ 0x1b60cece589da1d2, 0x00000001 },
		{ 0x01fcb42be1453f5b, 0x0000004f },
		{ 0x007a3f2457df0749, 0x0000013f },
		{ 0x0001363130e3ec7b, 0x000017aa },
		{ 0x0000f66745411d8a, 0x0000b063 },
		{ 0x00001c757dfab350, 0x00048863 },
		{ 0x000003dc4979c652, 0x00224ea7 },
		{ 0x000000159edc3144, 0x06409ab3 },
		{ 0x000000011eadfee3, 0xa99c48a8 },
	},
};

static inline bool test_div64_verify(u64 quotient, u32 remainder, int i, int j)
{
	return (quotient == test_div64_results[i][j].quotient &&
		remainder == test_div64_results[i][j].remainder);
}

/*
 * This needs to be a macro, because we don't want to rely on the compiler
 * to do constant propagation, and `do_div' may take a different path for
 * constants, so we do want to verify that as well.
 */
#define test_div64_one(dividend, divisor, i, j) ({			\
	bool result = true;						\
	u64 quotient;							\
	u32 remainder;							\
									\
	quotient = dividend;						\
	remainder = do_div(quotient, divisor);				\
	if (!test_div64_verify(quotient, remainder, i, j)) {		\
		pr_err("ERROR: %016llx / %08x => %016llx,%08x\n",	\
		       dividend, divisor, quotient, remainder);		\
		pr_err("ERROR: expected value              => %016llx,%08x\n",\
		       test_div64_results[i][j].quotient,		\
		       test_div64_results[i][j].remainder);		\
		result = false;						\
	}								\
	result;								\
})

/*
 * Run calculation for the same divisor value expressed as a constant
 * and as a variable, so as to verify the implementation for both cases
 * should they be handled by different code execution paths.
 */
static bool __init test_div64(void)
{
	u64 dividend;
	int i, j;

	for (i = 0; i < SIZE_DIV64_DIVIDENDS; i++) {
		dividend = test_div64_dividends[i];
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_0, i, 0))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_1, i, 1))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_2, i, 2))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_3, i, 3))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_4, i, 4))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_5, i, 5))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_6, i, 6))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_7, i, 7))
			return false;
		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_8, i, 8))
			return false;
		for (j = 0; j < SIZE_DIV64_DIVISORS; j++) {
			if (!test_div64_one(dividend, test_div64_divisors[j],
					    i, j))
				return false;
		}
	}
	return true;
}

static int __init test_div64_init(void)
{
	struct timespec64 ts, ts0, ts1;
	int i;

	pr_info("Starting 64bit/32bit division and modulo test\n");
	ktime_get_ts64(&ts0);

	for (i = 0; i < TEST_DIV64_N_ITER; i++)
		if (!test_div64())
			break;

	ktime_get_ts64(&ts1);
	ts = timespec64_sub(ts1, ts0);
	pr_info("Completed 64bit/32bit division and modulo test, "
		"%llu.%09lus elapsed\n", ts.tv_sec, ts.tv_nsec);

	return 0;
}

static void __exit test_div64_exit(void)
{
}

module_init(test_div64_init);
module_exit(test_div64_exit);

MODULE_AUTHOR("Maciej W. Rozycki <macro@orcam.me.uk>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("64bit/32bit division and modulo test module"