Not doing something to the outcome of both sub‘s relies on the byte wraparound and can only works as long as unsigned logic is used via jbe and friends. This is the simplest code you can write to differentiate between any case letters and all the rest: sub al, ‘A’ cmp al, ‘Z’-‘A’ jbe Letter … Read more
1) x86 probably the worst instruction set to learn first. just because you have one is not a good reason (you may not know it but for every x86 you have several arm processors not that using those is a good idea either). 2) start with a simulator, bare metal makes it a lot easier…pcemu … Read more
how to input floating point numbers in assembly language… and how to add subtract and multiply these floating point numbers [closed] solved how to input floating point numbers in assembly language… and how to add subtract and multiply these floating point numbers [closed]
No, the “high-end” feature that matters on those ARM CPUs is out-of-order execution, with branch-prediction + speculative execution. In-order CPUs with NEON (like Cortex A-53) aren’t on the list of affected CPUs, because Spectre depends on speculative execution. Spectre primes the branch predictors so an indirect branch in privileged code is mispredicted to go somewhere … Read more
Even I get an warning a function returns an address from local variable, it compiles. Isn’t it then UB of compiler? No, but if it were, how could you tell? You seem to have a misunderstanding of undefined behavior. It does not mean “the compiler must reject it”, “the compiler must warn about it”, “the … Read more
Those two lines are checking for a “negative” sign on either of the 16 bit zoned or unpacked decimal numbers, which contain one decimal digit per byte (bcd – binary coded decimal) in the low order bits (bits 0 to 3). The sign is stored in bits 4 through 7 of the least significant byte. … Read more
This code prints a prompt and inputs a number. It then prints that number of lines of stars. On the first line is 1 star, the second line 2 stars, and so on. I have annotated the code to make it more clear. The code does this with two nested loops. The ecx register is … Read more
This is how you do it. Next code was made with Visual Studio 2010 C++ console project. First, the assembly part, pay attention to the comments, how to get the string’s address from stack, how the characters are visited, and the most important part, how the undesired chars are deleted: .386 .model flat, C .code … Read more
There’s no single instruction that can do this. BMI1 blsi dst,src can isolate the lowest set bit, not the highest. i.e. x & -x. If x86 had a bit-reversed version of blsi, we could use that, but it doesn’t. But you can do much better than what you were suggesting. An all-zero input is always … Read more
att vs intel syntax has been covered many times, here and other places. Assembly language is a language defined by the assembler, the particular program used to convert the ASCII assembly language into machine code for the particular target you are interested in. Unlike say a C or C++ compiler where there is a standard … Read more
Your code could be simplified a lot (and simpler code usually means that it’s simpler to find any mistakes). Here’s an outline of an easier way of doing this (I’ll leave it up to you to implement it in x86 assembly): void to_bin_string(unsigned input) { char output[33]; // The number of binary digits needed to … Read more
How come x86 works on 64-bit Windows 7, Windows 8, and even the server configuration machines that are in 64 bit OS? Because of WoW64 (Windows on Windows 64-bit). Basically, it is a 32 bit emulator, which allows you to run 32 bit programs in a 64 bit operating system. X86 vs X64 vs Any … Read more
Many ways to do this, of course. If you decide to use the hardware parity flag, keep in mind that it only checks the low 8 bits. A solution using this approach might be to process your 32 bit input as four 8 bit values, and use XOR on the partial results: p(31:0) = p(31:24) … Read more
The answer to this question can be very easily found by looking at the proper page of the Intel 64 and IA-32 Instruction Set Reference. In this case, you’re looking for the MUL and DIV instructions (in case you’re operating on unsigned operands) or IMUL and IDIV instructions, which are used for signed integer multiplication … Read more
Instruction size does not related to data or address bus size. Some 16-bit x86 CPUs have 3 totally different sizes with 8-bit data bus, 20-bit address bus and variable length instruction size. Modern 32-bit or 64-bit x86 have variable length instruction too for backward compatibility. Just look at the movl $0x542412e6, %eax and pushl 0x08048dd6 … Read more