If it is possible for you to use architecture specific instructions you'll likely be able to accelerate the operation beyond what is possible using bit-twiddeling hacks: For example if you write code for the Intel Haswell and later CPUs you can use the BMI2 instruction set which contains the pext... As you've sort of realized, you're trying to compile assembly for a 32 bit machine, on a 64 bit machine. How fetch_assoc know that you want the next row from the table? In 32 bit and 64 bit code segments it is 32 bit. ; float dist(float *x, float *y, int length) ; in xmm0 there is *x, in xmm1 float *y, in rdi there is length Actually, rdi is *x, rsi is *y and rdx is length. Thus, to switch to ring3, you should use 0x0b. mov [0200h], ax mov [0202h], ax Add a segment override prefix is the segment is addressable through ES. Use instructions like the following if the segment is addressable through the DS segment register. Why is it so? This means that in total, in the address space, 2 ^ 64 bytes can... Read the documentation. For returning a value in EAX you have to declare it as an integer type. x64 program returns the correct SIDT value occasionally (x64 assembly). You can use this tool to learn how x86 instructions are encoded or to help with Your immediate problem is cmpb '\n', %al which is missing the $ sign required in at&t syntax to make it an immediate. Read the abi documentation or... Let's start with the first question. A easy way is using the aad instruction. If OS is 64 bit and your application is 32 bit you can get Program Files folder using an environment variable (actually there is a special - unsupported in Environment.SpecialFolder - constant in SHGetSpecialFolderLocation but it's easier like this): Environment.GetEnvironmentVariable("ProgramW6432"); Just check your OS is 64 bit (in 32 bit... You've made a classic mistake, attempting performance analysis on non-optimized code. movswl 12(%ebp), %edx brings your short b in the %EDX register. It isn't explicitly stated, but I think we can assume we're dealing with little-endian here (every PC you'll get to use today will use that). How many words can be in the address space? share | improve this answer | follow | answered Jun 20 '11 at 9:30. What do the /r, /0, /2, and /4 characters mean in x64 Opcodes? VM Design: More opcodes or less opcodes? Note that opcodes can specify that the REG field in the ModR/M byte is fixed at a particular value. The issue wasn't 64bit, it was a timing/focus issue. Why do these two instructions have the same opcode? None of them are incorrect. PlaySound function pszSound A string that specifies the sound to play. movl 8(%ebp), %eax brings your int a in the %EAX register. I assume /r means a ModR/M byte but what do /0 /2 and /4 mean? The default operand size is defined by the current operating mode, and you can toggle using a 0x66 prefix.
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