C STANDARD UNDEFINED BEHAVIOR VERSUS WITTGENSTEIN 1. DEPRESSING AND FAINTLY TERRIFYING Chris Lattner, the architect of the Clang/LLVM C compiler explained the effects of the C standard’s “undefined behavior”(UB): UB is an inseperable part of C programming, […] this is
Via @johnregehr this further tale of compiler “optimizations” that break correct C code without even a warning by deleting a necessary null pointer check. In this example, Bar contains a stack of Foos. Sometimes the Foo stack is empty, so
Distributed computation involves many interesting issues concerning shared data. Here I want to sketch out what networks look like using applied (informal) mathematics so we can look at some algorithms for consensus and data consistency. No formal methods or category
Originally Nov 30, 2017. (revised 2021,2023) Russell introduced what is often viewed as his most original contribution to mathematical logic: his theory of types—which in essence tries to distinguish between sets, sets of sets, etc. by considering them to be
From the LLVM developer mailing list this remarkable exchange in which Chris Lattner of LLVM says that the compiler use of undefined behavior (UB) is so “crappy” that the only solution is to abandon C programming (my bold). On Jul
The Kafkaesque interaction of the C standard and the main open source C compilers was concisely outlined by one of the main LLVM authors back in 2011: “knowing that INT_MAX+1 is undefined allows optimizing X+1 > X to “true”. Knowing
Consider the following code: void f(void) { unsigned char x[1]; /* intentionally uninitialized */ x[0] ^= x[0]; printf(“%d\n”, x[0]); printf(“%d\n”, x[0]); return; } In this example, the unsigned char array x is intentionally uninitialized but cannot contain a trap representation because it has a
The Chang-Maxemchuk algorithm (US Patent 4,725,834 ) solves atomic broadcast (and in-order broadcast) problems for distributed networks in a far simpler and more efficient way than some popular alternatives. In fact, the obscurity of this method is hard to understand given the
Regarding ease-of-use, it’s often struck me when reviewing data systems papers that the evaluation sections are full of performance and correctness criteria, but only rarely is there any discussion of how well a system helps its target users achieve their
All of the distributed consensus algorithms I have been reviewing recently (Paxos, Raft, Zab, Chang Maxemchuck, Viewstamped, … ) are based on a number of assumptions about the network environment, including the assumption that messages may be lost but are