<!-- SVP64 Butterfly DCT Instructions here described are based on -->

<!-- PLEASE NOTE THESE ARE UNAPPROVED AND DRAFT, NOT SUBMITTED TO OPF ISA WG -->

# [DRAFT] Integer Butterfly Multiply Add/Sub FFT/DCT

A-Form

* maddsubrs  RT,RA,RB,SH

Pseudo-code:

    n <- XLEN-SH
    sum <- (RT) + (RA)
    diff <- (RT) - (RA)
    prod1[0:(XLEN*2)-1] <- MULS(RB, sum)
    prod2[0:(XLEN*2)-1] <- MULS(RB, diff)
    res1 <- prod1[XLEN/2-SH:XLEN-1-SH]
    res2 <- prod2[XLEN/2-SH:XLEN-1-SH]
    RT <- (RT) + EXTS(res1)
    RS <- (RS) + EXTS(res2)

Special Registers Altered:

    None