## addsd - add scalar double (64 bit floating point)

    dest = dest + source

The addsd instruction adds the source value (second operand) to the destination (an XMM register). The source can be an XMM register or a 64 bit memory location. There is also vaddsd on CPUs with AVX instructions which allows using 3 XMM registers or 2 XMM registers and a memory location which can simplify coding.

            addsd   xmm0, xmm1          ; add xmm1 to xmm0
                                        ; leave the rest of xmm0 as is
            addsd   xmm0, [x]           ; add 64 bit variable x to xmm0
                                        ; leave the rest of xmm0 as is
            addsd   xmm0, [rsi]         ; add 64 bit value [rsi] to xmm0
                                        ; rsi holds the address of a double
                                        ; leave the rest of xmm0 as is
            vaddsd  xmm3, xmm0, xmm15   ; xmm3 = xmm0 + xmm15

                ; Note: operates by copying 128 bits from xmm0 to xmm3
                ; before adding.  This might occasionally be useful.
                ; The rest of ymm0 is left as is
                ; using addsd would change either xmm0 or xmm15
                ; possibly requiring an additional instruction

            vaddsd  xmm3, xmm0, [x]     ; xmm3 = xmm0 + x

### flags: none