Page 101 - ARM 64 Bit Assembly Language

Data processing and other instructions 87

4.2.1.1 Syntax

<op>{s} Rd, Rn, <Operand2>
<op2>{s} Rd, Rn, Rm
neg{s} Rd, <Operand2>
ngc{s} Rd, Rm

• <op> is one of add, sub.
• <op2> is one of adc, sbc. The carry bit from PSTATE is added to the two operands.
• neg and ngc are aliases of sub and sbc where Rn is ZR. Therefore, neither syntax uses
Rn.
• The optional s specifies whether or not the instruction should affect the bits in PSTATE.

4.2.1.2 Operations

Name Effect Description
add Rd ← Rn + Operand2 Add.
adc Rd ← Rn + Rm + carry Add with carry.
sub Rd ← Rn − Operand2 Subtract.
sbc Rd ← Rn − Rm + carry − 1 Subtract with carry.
neg Rd ←−Operand2 Negate.
ngc Rd ←−Rn + carry − 1 Negate with carry.

4.2.1.3 Examples

1 add x0, x1, x2 // x0 = x1 + x2 and don’t set PSTATE
2
3 subs x3, x3, #1 // x3 = x3 - 1 and set nzcv flags in PSTATE
4
5 neg x4, x5, lsl #4 // x4 = -(x5 << 4)

Example 9. The following listings show a complete program for adding the contents of two
statically allocated variables and printing the result. The printf() function expects to find
the address of a string in x0, as it prints the string, it finds the %d formating command, which
indicates that the value of an integer variable should be printed. It expects the variable to be
stored in w1. Note that the variable sum does not need to be stored in memory. It is stored in
w1,where printf() expects to find it.