## addpd - add packed doubles (64 bit floating point)

    dest[0] = dest[0] + source[0]
    dest[1] = dest[1] + source[1]

The addpd instruction adds the 2 source values (second operand) to the 2 values of the destination (an XMM register). The source can be an XMM register or a 64 bit memory location. There is also vaddpd on CPUs with AVX instructions which allows using 3 XMM registers or 2 XMM registers and a memory location which can simplify coding and which adds 4 pairs of values iy you use YMM registers.

            addpd   xmm0, xmm1          ; add 2 pairs of values from xmm1 to xmm0
                                        ; leave the rest of ymm0 as is
            addpd   xmm0, [x]           ; add 2 pairs of values from x to xmm0
                                        ; x is an array of doubles
                                        ; leave the rest of ymm0 as is
            addpd   xmm0, [x+8*r9]      ; add 2 pairs from xmm0 and the array x
                                        ; r9 contains the first index of x to use
                                        ; leave the rest of ymm0 as is
            vaddpd  xmm3, xmm0, xmm15   ; add 2 pairs of values from xmm0 & xmm15
                                        ; store results in xmm3
            vaddpd  ymm3, ymm0, [x]     ; add 4 pairs of values from ymm0 & x
                                        ; x is a double array
                                        ; store results in ymm3
            vaddpd  ymm3, ymm0, [rsi]   ; add 4 pairs of values from ymm0 & [rsi]
                                        ; rsi contains the address of a double array
                                        ; store results in ymm3

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