jxu

These are simplified examples I came up with to go along with William Woodruff's excellent blog post on x86-64 addressing modes.

All the examples are compiled with GCC -O3 or -Os, which is indicative of what the compiler thinks the best option is in practice.

Base + Index

Use case: Indexing into a byte array (whose address is not fixed)

char f(char buf[], int index)

jxu

f(std::vector<bool, std::allocator<bool>> const&, unsigned long):
        mov     rax, rdi                    ; rax = v
        mov     rdi, rsi                    ; rdi = i
        mov     ecx, esi			        ; rcx = i
        mov     rdx, QWORD PTR [rax]	    ; rdx = *v
        shr     rdi, 6				        ; rdi >>= 6
        mov     eax, 1				        ; rax = 1
        sal     rax, cl				        ; rax <<= (rcx & 0xFF)
        and     rax, QWORD PTR [rdx+rdi*8]	; rax &= rdx[rdi]
        setne   al				            ; al = (rax != 0)

jxu

# usage: ./spelling_bee uablmnt
# first letter is central
grep -P "^(?=.*${1:0:1})[$1]{4,}$" /usr/share/dict/words

jxu

/**
 * Simple Vector class, extending built-in Arrays
 * @extends Array
 */
class Vector extends Array {
    /**
     * Create Vector.
     * @param {Array} array - Array to be unpacked and used to create Vector.
     *
     * This behavior is the same for length 1 Array.

jxu

// My own buffered versions of fgetc, fputc
// After done writing, output has to be flushed manually

#pragma once
#include <stdio.h>
#include <stdint.h>

#define INBUF_SIZE 8192
#define OUTBUF_SIZE 8192