Fix undefined behavior in fixed point number conversion and random_int #3143
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Apr 10, 2022
4971: Fix undefined behavior in fixed point number conversion r=def- a=Robyt3 See #4970: ``` /home/runner/work/ddnet/ddnet/src/base/math.h:50:11: runtime error: left shift of negative value -32 #0 0x198d955 in i2fx(int) /home/runner/work/ddnet/ddnet/src/base/math.h:50:11 #1 0x197ebdf in CLayerQuads::NewQuad(int, int, int, int) /home/runner/work/ddnet/ddnet/src/game/editor/layer_quads.cpp:47:22 #2 0x18ef8d3 in CEditor::Init() /home/runner/work/ddnet/ddnet/src/game/editor/editor.cpp:6360:18 #3 0xa8e5be in CClient::Run() /home/runner/work/ddnet/ddnet/src/engine/client/client.cpp:2917:13 #4 0xaf6726 in main /home/runner/work/ddnet/ddnet/src/engine/client/client.cpp:4458:11 #5 0x7fadd9e610b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x240b2) #6 0x43cefd in _start (/home/runner/work/ddnet/ddnet/san/DDNet+0x43cefd) ``` Upstream teeworlds/teeworlds#3143. ## Checklist - [X] Tested the change ingame (on upstream) - [ ] Provided screenshots if it is a visual change - [ ] Tested in combination with possibly related configuration options - [ ] Written a unit test if it works standalone, system.c especially - [ ] Considered possible null pointers and out of bounds array indexing - [X] Changed no physics that affect existing maps - [X] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional) Co-authored-by: Robert Müller <robytemueller@gmail.com>
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fx2iandi2fx) is undefined behavior. The shifts are replaced with equivalent multiplication and division.random_int()function may shift a bit into the sign bit, which is undefined behavior. The masks are adjusted so this is no longer the case.