STOSD
instruction
1.Stores
a dword value from EAX into memory location the address of which is in EDI (D - destination).
2.After
the value from EAX is transferred it increments EDI by 4 (EDI now points to the next DWORD in memory) if DF flag is 0.
If DF
flag is 1 then EDI value decremented by 4 (EDI now points to the previous DWORD in memory)
REP
prefix
Causes the next instruction to be repeated until the
count in ECX register is decremented to
0
Example: zeroing all memory (will trap because of
access violation)
XOR EAX,EAX ;
fill with 0
MOV EDI, 0 ; starting address, XOR EDI, EDI
MOV ECX, 0xFFFFFFFF / 4 ;
0x3FFFFFFF dwords
REP STOSD