Every Bitcoin transaction consists of two main components: Inputs (UTXOs): Unspent Transaction Outputs from previous transactions that you’re now spending. These are references to outputs you received earlier. Think of them as specific bills from your wallet you’re handing over. Outputs: The destinations and amounts for the Bitcoin. This includes the recipient’s address and the…
The x86-64 ISA provides ucomiss and ucomisd for comparing SSE floating-point values. These instructions compute S1 – S2 and set the EFLAGS register (ZF, PF, CF) based on the result. Instruction Operands Purpose ucomiss S2, S1 Compare single-precision (32-bit) floats ucomisd S2, S1 Compare double-precision (64-bit) floats In AT&T syntax, the source operand is listed…
Exit codes are how programs communicate success or failure to the shell and parent processes. Understanding them is essential for writing reliable scripts and debugging applications. Linux and Windows handle these differently, so knowing both conventions matters if you work across platforms. Linux Exit Codes On Linux, the convention is simple: 0 means success, 1–255…
To generate native assembly code (x86-64 asm, ARM64, etc.) from OCaml’s native compiler, use the -S flag along with other optimization-related options: ocamlopt -S -inline 20 -nodynlink not.ml -o not.opt This produces a .s file containing the generated assembly. The flags break down as: -S — Stop after assembly generation and keep the .s file…
Before encoding instructions, you need to understand the two assembly syntaxes you’ll encounter—they differ fundamentally in operand order and addressing format. Intel syntax (Intel/AMD manuals): Operand order: destination, source Memory addressing: [base+offset] Example: add r8, [rdi+0xa] AT&T syntax (GNU toolchains on Linux): Operand order: source, destination Memory addressing: offset(%base) Example: addq 0xa(%rdi), %r8 For most…
Measuring time accurately matters for performance profiling, benchmarking, and latency-sensitive applications. Linux provides several APIs with different tradeoffs in resolution, overhead, and reliability. Understanding which to use prevents subtle bugs in production code. POSIX Time APIs: gettimeofday and clock_gettime gettimeofday() and clock_gettime() are the standard POSIX calls for reading system time. gettimeofday() returns seconds and…
GCC allows you to embed assembly code directly in C/C++ programs through inline assembly (asm and __asm__). This is useful when you need fine-grained control over processor execution—forcing variables into specific registers, reading CPU state efficiently, or hand-optimizing critical sections verified by profiling. Basic Syntax GCC uses AT&T syntax by default on x86/x86-64. The simplest…
When debugging and optimizing C/C++ programs, you need to see how the compiler translates your source code into assembly. A mixed source and assembly listing lets you trace exactly what machine instructions correspond to each line of your source. Using objdump (Recommended Modern Approach) The most straightforward method is to compile with debugging symbols and…