design.md

Notation

• define the functions

  SWAPMOVE32_X(x,y,m,n) {
    t <- y ^ ( x >> n )
    t <- t & m
    x <- x ^ ( t << n )
  
    return x
  }
  
  SWAPMOVE32_Y(x,y,m,n) {
    t <- y ^ ( x >> n )
    t <- t & m
    y <- y ^ ( t      )
  
    return y
  }
  

  i.e., a 32-bit variants of SWAPMOVE.

Options

${ARCH}	${ALG}	${IMP}	Symbol	Meaning
	elephant	rv32	ELEPHANT_RV32_UNROLL	use fully (vs. partially, by a factor of two) unrolled implementation
	elephant	rv32	ELEPHANT_RV32_TYPE1	select 32-bit RISC-V base ISA: option 1, per description below
	elephant	rv32	ELEPHANT_RV32_TYPE2	select 32-bit RISC-V base ISA plus ISE: option 2, per description below

${IMP} = "rv32"

• ELEPHANT_RV32_TYPE1: base ISA.

• ELEPHANT_RV32_TYPE2: base ISA plus ISE.

  elephant.pstep.x rd, rs1, rs2, imm {
    x       <- GPR[rs1]
    y       <- GPR[rs2]
  
    if      ( imm == 0 ) { 
      r <- SWAPMOVE32_X( x, y, 0x000000FF,  8 )
    }
    else if ( imm == 1 ) {
      r <- SWAPMOVE32_X( x, y, 0x000000FF, 16 )
    }
    else if ( imm == 2 ) {
      r <- SWAPMOVE32_X( x, y, 0x000000FF, 24 )
    }
    else if ( imm == 3 ) {
      r <- SWAPMOVE32_X( x, y, 0x0000FF00,  8 )
    }
    else if ( imm == 4 ) {
      r <- SWAPMOVE32_X( x, y, 0x000000FF, 24 ) >>> 24
    }
    else if ( imm == 5 ) {
      r <- SWAPMOVE32_X( x, y, 0x0000FF00, 16 ) >>> 16
    }
    else if ( imm == 6 ) {
      r <- SWAPMOVE32_X( x, y, 0x00FF0000,  8 ) >>>  8
    }
  
    GPR[rd] <- r
  }
  
  elephant.pstep.y rd, rs1, rs2, imm {
    x       <- GPR[rs1]
    y       <- GPR[rs2]
  
    if      ( imm == 0 ) { 
      r <- SWAPMOVE32_Y( x, y, 0x000000FF,  8 )
    }
    else if ( imm == 1 ) {
      r <- SWAPMOVE32_Y( x, y, 0x000000FF, 16 )
    }
    else if ( imm == 2 ) {
      r <- SWAPMOVE32_Y( x, y, 0x000000FF, 24 )
    }
    else if ( imm == 3 ) {
      r <- SWAPMOVE32_Y( x, y, 0x0000FF00,  8 )
    }
    else if ( imm == 4 ) {
      r <- SWAPMOVE32_Y( x, y, 0x000000FF, 24 )
    }
    else if ( imm == 5 ) {
      r <- SWAPMOVE32_Y( x, y, 0x0000FF00, 16 )
    }
    else if ( imm == 6 ) {
      r <- SWAPMOVE32_Y( x, y, 0x00FF0000,  8 )
    }
  
    GPR[rd] <- r
  }
  
  elephant.sstep   rd, rs1           {
    x       <- GPR[rs1]
  
    r       <- SBOX[ x_{31..28} ] || SBOX[ x_{27..24} ] ||
               SBOX[ x_{23..20} ] || SBOX[ x_{19..16} ] ||
               SBOX[ x_{15..12} ] || SBOX[ x_{11.. 8} ] ||
               SBOX[ x_{ 7.. 4} ] || SBOX[ x_{ 3.. 0} ] 
               
    r       <- SWAPMOVE32( r, 0x0A0A0A0A,  3 )
    r       <- SWAPMOVE32( r, 0x00CC00CC,  6 )
    r       <- SWAPMOVE32( r, 0x0000F0F0, 12 )
    r       <- SWAPMOVE32( r, 0x0000FF00,  8 )
  
    GPR[rd] <- r
  }