The dword ptr part is called a size directive. This page explains them, but it wasn't possible to direct-link to the correct section.
Basically, it means "the size of the target operand is 32 bits", so this will bitwise-AND the 32-bit value at the address computed by taking the contents of the ebp register and subtracting four with 0.
Consider the figure enclosed in this other question. ebp-4 is your first local variable and, seen as a dword pointer, it is the address of a 32 bit integer that has to be cleared. Maybe your source starts with
Object x = null;
It is a 32bit declaration. If you type at the top of an assembly file the statement [bits 32], then you don't need to type DWORD PTR. So for example:
[bits 32]
.
.
and [ebp-4], 0
Follow WeChat
Success story sharing
Want to stay one step ahead of the latest teleworks?
Subscribe Now相似问题
- What are the differences between a pointer variable and a reference variable?
- What is a smart pointer and when should I use one?
- What is the difference between const int*, const int * const, and int const *?
- What does "dereferencing" a pointer mean?
- Why doesn't GCC optimize a*a*a*a*a*a to (a*a*a)*(a*a*a)?
- Why are elementwise additions much faster in separate loops than in a combined loop?
- Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
PTRpart needed? Isn't dword enough to encode the size? NASM does not useptrAFAIK.Modern processors, including embedded systems, usually have a word size of 8, 16, 24, 32, or 64 bits, while modern general purpose computers usually use 32 or 64 bits.en.wikipedia.org/wiki/Word_(computer_architecture)PTRis needed?