I wrote librdrand. It’s a very basic set of routines to use the RdRand instruction to fill buffers with random numbers. The performance data we showed at IDF is from test software I wrote that spawns a number of threads using pthreads in Linux. Each thread pulls fills a memory buffer with random numbers using … Read more
Well, first of all, jmp simply ‘jumps’ to the label that you give to it (which is a memory address as program instructions are stored in memory) while call stores the location where it will return (below the call instruction) in the stack, jmp to the label, and then at the ret instruction, jmp back … Read more
Use this function to print them: #include <stdint.h> #include <string.h> void print128_num(__m128i var) { uint16_t val[8]; memcpy(val, &var, sizeof(val)); printf(“Numerical: %i %i %i %i %i %i %i %i \n”, val[0], val[1], val[2], val[3], val[4], val[5], val[6], val[7]); } You split 128bits into 16-bits(or 32-bits) before printing them. This is a way of 64-bit splitting and … Read more
Accessing raw CPUID information is actually very easy, here is a C++ class for that which works in Windows, Linux and OSX: #ifndef CPUID_H #define CPUID_H #ifdef _WIN32 #include <limits.h> #include <intrin.h> typedef unsigned __int32 uint32_t; #else #include <stdint.h> #endif class CPUID { uint32_t regs[4]; public: explicit CPUID(unsigned i) { #ifdef _WIN32 __cpuid((int *)regs, (int)i); … Read more
General claim is modern systems have better branch predictors and compilers are much more advanced so their cost on instruction encoding space is not justified. This is from ARMv8 Instruction Set Overview The A64 instruction set does not include the concept of predicated or conditional execution. Benchmarking shows that modern branch predictors work well enough … Read more
It’s AT&T assembly syntax: source comes before destination mnemonic suffixes indicate the size of the operands (q for quad, etc.) registers are prefixed with % and immediate values with $ effective addresses are in the form DISP(BASE, INDEX, SCALE) (DISP + BASE + INDEX * SCALE) Indirect jump/call operands indicated with * (as opposed to … Read more
JNZ is short for “Jump if not zero (ZF = 0)”, and NOT “Jump if the ZF is set”. If it’s any easier to remember, consider that JNZ and JNE (jump if not equal) are equivalent. Therefore, when you’re doing cmp al, 47 and the content of AL is equal to 47, the ZF is … Read more
Something I found: * EAX – Accumulator Register * EBX – Base Register * ECX – Counter Register * EDX – Data Register * ESI – Source Index * EDI – Destination Index * EBP – Base Pointer * ESP – Stack Pointer
Carry Flag The rules for turning on the carry flag in binary/integer math are two: The carry flag is set if the addition of two numbers causes a carry out of the most significant (leftmost) bits added. 1111 + 0001 = 0000 (carry flag is turned on) The carry (borrow) flag is also set if … Read more
You can absolutely make a c program from assembler. The problem is it may not look like what you are thinking, or maybe it will. My PIC is rusty but using another assembler, say you had add r1,r2 In C lets say that becomes r1 = r1 + r2; Possibly more readable. You lose any … Read more