Potential false positive - duplicateExpression

[Cez Chi]

Hi, I have the following loop which gives me a [duplicateExpression] and a [unsignedPositive] false positives, which I think are related:

const uint32_t time_out = some_value;
uint32_t start_time = get_time_ms();
uint32_t elapsed = 0;

while (elapsed <= time_out) {
    do_something_until_timeout();
    // Update elapsed time.
    elapsed = get_time_ms() - start_time;
}

I think it is because cppcheck doesn't know that get_time_ms() returns a different value everytime. Is there a way to fix this or should I ignore it? Or maybe I did a silly mistake that I overlooked.

[CHR]

Can you post a minimal example which reproduces the problem?

[Cez Chi]

Hi, apologies for the late reply. Here is a minimal example which reproduces the problem:

static void wait(const HAL* hal, const uint32_t time_out) {
    uint32_t start_time = hal->get_time_ms();
    uint32_t elapsed = 0;

    while (elapsed <= time_out) {
        // Update elapsed time.
        elapsed = hal->get_time_ms() - start_time;
    }
}

[CHR]

I only get one FP:

foo.cpp:26:20: style: Unsigned expression 'time_out' can't be negative so it is unnecessary to test it. [unsignedPositive]
    while (elapsed <= time_out) {
                   ^
foo.cpp:24:24: note: Assignment 'elapsed=0', assigned value is 0
    uint32_t elapsed = 0;
                       ^
foo.cpp:26:20: note: Unsigned positive
    while (elapsed <= time_out) {
                   ^

Ticket is here: https://trac.cppcheck.net/ticket/11982