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include: util: fix division by zero in DIV_ROUND macros #95303

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include: util: fix division by zero in DIV_ROUND macros #95303

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23 changes: 17 additions & 6 deletions include/zephyr/sys/util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -339,20 +339,30 @@ extern "C" {
#define WB_DN(x) ROUND_DOWN(x, sizeof(void *))

/**
* @brief Divide and round up.
* @brief Divide and round up towards infinity, akin to ceil().
*
* @note Works with negative operands, asserts if denominator is zero.
*
* Example:
* @code{.c}
* DIV_ROUND_UP(3, 0); // Asserts
* DIV_ROUND_UP(1, 2); // 1
* DIV_ROUND_UP(3, 2); // 2
* DIV_ROUND_UP(-3, -2); // 2
* DIV_ROUND_UP(3, -2); // 1
* DIV_ROUND_UP(-3, 2); // 1
* @endcode
*
* @param n Numerator.
* @param d Denominator.
*
* @return The result of @p n / @p d, rounded up.
*/
#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
#define DIV_ROUND_UP(n, d) ((d == 0) \
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@pdgendt pdgendt Sep 25, 2025 •
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How about:

#define DIV_ROUND_UP(n, d) ({                                                                      \
		__typeof__(n) un = (n);                                                            \
		__typeof__(d) ud = (d);                                                            \
		__ASSERT_NO_MSG(ud != 0);                                                          \
		((un + ud - 1) / ud);                                                              \
	})

Inspired by #96478

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CC: @fabiobaltieri

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@fabiobaltieri fabiobaltieri Sep 25, 2025 •
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Nah :-(

include/zephyr/drivers/can.h:           uint32_t data_32[DIV_ROUND_UP(CAN_MAX_DLEN, sizeof(uint32_t))];
include/zephyr/logging/log_msg.h:       long long _ll_buf[DIV_ROUND_UP(len, sizeof(long long))]; \
include/zephyr/logging/log_msg.h:       long double _ld_buf[DIV_ROUND_UP(len, sizeof(long double))]; \

and plenty more, I think we should have a DIV_ROUND_UP and div_round_up, once you do the ({ thing it effectively becomes a function

? __ASSERT_NO_MSG(false) \
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Looking closer at this, this won't work. The ternary operator won't be able to expand the macro for asserts here.

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We will have to use a static inline function then, but that needs a fixed type for return and parameters.

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You might need to resort to _Generic to make it work.

: ((((n % d) == 0) || ((n < 0) ^ (d < 0))) \
? (n / d) \
: (n / d) + 1))

/**
* @brief Divide and round to the nearest integer.
Expand All @@ -369,10 +379,11 @@ extern "C" {
*
* @return The result of @p n / @p d, rounded to the nearest integer.
*/
#define DIV_ROUND_CLOSEST(n, d) \
(((((__typeof__(n))-1) < 0) && (((__typeof__(d))-1) < 0) && ((n) < 0) ^ ((d) < 0)) \
? ((n) - ((d) / 2)) / (d) \
: ((n) + ((d) / 2)) / (d))
#define DIV_ROUND_CLOSEST(n, d) ((d == 0) \
? __ASSERT_NO_MSG(false) \
: (((((__typeof__(n))-1) < 0) && (((__typeof__(d))-1) < 0) && ((n) < 0) ^ ((d) < 0)) \
? ((n) - ((d) / 2)) / (d) \
: ((n) + ((d) / 2)) / (d)))

#ifndef MAX
/**
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10 changes: 10 additions & 0 deletions tests/unit/util/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -681,6 +681,16 @@ ZTEST(util, test_DIV_ROUND_UP)
zassert_equal(DIV_ROUND_UP(0, 1), 0);
zassert_equal(DIV_ROUND_UP(1, 2), 1);
zassert_equal(DIV_ROUND_UP(3, 2), 2);
zassert_equal(DIV_ROUND_UP(-3, -2), 2);
zassert_equal(DIV_ROUND_UP(3, -2), 1);
zassert_equal(DIV_ROUND_UP(-3, 2), 1);
}

ZTEST(util, test_assert_DIV_ROUND_UP_and_DIV_ROUND_CLOSEST)
{
ztest_set_assert_valid(true);
DIV_ROUND_UP(3, 0);
DIV_ROUND_CLOSEST(3, 0);
}

ZTEST(util, test_DIV_ROUND_CLOSEST)
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