False Positive: knownConditionTrueFalse with unsigned integers

[David Gibson]

With --enable=all 2.12.0, 2.12.1 and current git (6773cdb34bb4697a41c4438ebb2a34c4e4de4b69) all report knownConditionTrueFalse on the following code:

#define MIN(x, y)       (((x) < (y)) ? (x) : (y))

void example(unsigned int old_val)
{
    unsigned int new_val = MIN(old_val, 65535);

    if (!new_val) {
    }
}

This is clearly incorrect.

$ ~/src/cppcheck/cppcheck --enable=all example.c 
Checking example.c ...
example.c:7:6: style: Condition '!new_val' is always true [knownConditionTrueFalse]
 if (!new_val) {
     ^
example.c:5:25: note: Assignment 'new_val=((old_val)<65535)?old_val:65535', assigned value is less than 1
 unsigned int new_val = MIN(old_val, 65535);
                        ^
example.c:7:6: note: Condition '!new_val' is always true
 if (!new_val) {
     ^
example.c:3:0: style: The function 'example' is never used. [unusedFunction]
void example(unsigned int old_val)
^
Active checkers: 106/565

[Andrew C Aitchison]

This code passes with v2.9, but not v2.10 --enable=style

cppcheck-2.10 --enable=style TF.cpp
Checking TF.cpp ...
TF.cpp:7:13: style: Condition '!new_val' is always false [knownConditionTrueFalse]
if (!new_val) {
^
TF.cpp:5:32: note: Assignment 'new_val=((old_val)<65535)?old_val:65535', assigned value is less than 1
unsigned int new_val = MIN(old_val, 65535);
^
TF.cpp:7:13: note: Condition '!new_val' is always false
if (!new_val) {
^

[CHR]

Probably related to https://trac.cppcheck.net/ticket/11437