<!-- 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

DCTI-Form

* maddsubrs  RT,RA,RB,SH

Pseudo-code:

    sum <- (RT) + (RA)
    diff <- (RT) - (RA)
    prod1 <- MUL(RB, sum)
    prod2 <- MUL(RB, diff)
    res1 <- ROTL64(prod1, XLEN-SH)
    res2 <- ROTL64(prod2, XLEN-SH)
    RT <- (RT) + res1
    RS <- (RS) + res2

Special Registers Altered:

    None