signed overflow in "slider s32 full" demo widget

[jbarthelmes]

Version/Branch of Dear ImGui:

Dear ImGui 1.89.8 WIP (18974)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201703
define: _WIN32
define: _WIN64
define: __MINGW32__
define: __MINGW64__
define: __GNUC__=4
define: __clang_version__=16.0.1 (https://github.com/ziglang/zig-bootstrap bf1b2cdb83141ad9336eec42160c9fe87f90198d)
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK

My Issue/Question:

The demo widget "slider s32 full" creates an integer overflow that my compiler in debug traps with an illegal instruction. Signed overflow is UB IIRC.

Concretely, the issue is with v_range + 1 here:

imgui/imgui_widgets.cpp

Lines 2781 to 2782 in f7eea63

	if (!is_floating_point && v_range >= 0) // v_range < 0 may happen on integer overflows
	grab_sz = ImMax((float)(slider_sz / (v_range + 1)), style.GrabMinSize); // For integer sliders: if possible have the grab size represent 1 unit

With v_range for "slider s32 full" being 2147483647 = 2³¹-1.

[GamingMinds-DanielC]

Oh, quite true that, same for 64 bits. The expected behavior would be a division by a large negative number, resulting in a small negative number that then gets clamped to style.GrabMinSize, so no actual problem. But while the actual behavior is known, it technically is undefined, and that should be avoided.

@ocornut: replacing (float)(slider_sz / (v_range + 1)) with slider_sz / ((float)v_range + 1.0f)) should be safe there.

[jbarthelmes]

I changed the definition of v_range to float because the only other usage

imgui/imgui_widgets.cpp

Lines 2851 to 2852 in f7eea63

	if ((v_range >= -100.0f && v_range <= 100.0f) || tweak_slow)
	input_delta = ((input_delta < 0.0f) ? -1.0f : +1.0f) / (float)v_range; // Gamepad/keyboard tweak speeds in integer steps

treats it like float anyway. That makes it a one word change and the typecast on the division can also be removed.

[ocornut]

Merged b7a7d67, thanks!