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menu_book Course Curriculum (x86-64 Assembly) expand_more
Registers & Data
MOV register Immediate operand Memory operand LEA Byte word dword qword Zero extension MOVZX Sign extension MOVSX XCHG PUSH POP
Arithmetic
ADD SUB INC DEC IMUL MUL IDIV DIV NEG ADC
Bit Operations
AND OR XOR NOT SHL SHR SAR ROL ROR BT
Comparison & Branching
CMP TEST JMP JE and JZ JNE and JNZ JL signed JB unsigned JG signed JA unsigned CMOVcc
Loops & Arrays
Counter loop Pointer traversal Indexed addressing Scaled index Array sum Find maximum Linear search Byte scan Reverse buffer REP MOVSB
Functions & ABI
CALL RET Function prologue Function epilogue Argument registers Return value RAX Callee-saved registers Stack alignment Local stack storage Recursive function
Strings & System Calls
ASCII string Null terminator String length loop write syscall exit syscall read syscall File open syscall File close syscall Error return check Command line argc argv
Floating & SIMD
XMM registers MOVSS ADDSS MULSS MOVSD ADDSD Packed ADDPS PXOR Unaligned MOVDQU Horizontal sum pattern
x86-64 Assembly / Arithmetic

DEC

Learn DEC in x86-64 Assembly through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Beginner

DEC is an atomic x86-64 Assembly topic inside Arithmetic. This lesson focuses on how the DEC construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for DEC, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.

Topic-specific example

assembly-02-04-dec.asm
assembly Try It Live 
mov rcx, 4
dec rcx
Edge case / engineering note

For DEC, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

DEC Mastery Check →
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INC
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IMUL