###########################################
#
#  MacroMirror
#
#  Statically compute vertically or
#  horizontally mirrored copies of 8x8 sprites
#  using macros and the '@' operator.
#  These techniques generalize readily to
#  arbitrary-sized memory blocks.
#
#  John Earnest
#
###########################################

: main
	v1 := 10
	i := sprite-1 sprite v0 v0 8
	i := sprite-2 sprite v0 v1 8
	i := sprite-3 sprite v1 v0 8
	i := sprite-4 sprite v1 v1 8
	loop again

# see http://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith32Bits
:macro rev8 X { :byte { 0xFF & ( 0x10101 * ( 0x22110 & 0x0802 * X ) | 0x88440 & 0x8020 * X ) >> 16 } }

:macro mirror-v_        { :byte   { @ from + 7 - HERE - to }        }
:macro mirror-h_        { :calc t { @ from +     HERE - to } rev8 t }
:macro mirror-8 BASE OP { :calc to { HERE }  :calc from { BASE }  OP OP OP OP OP OP OP OP }
:macro mirror-v BASE    { mirror-8 BASE mirror-v_ }
:macro mirror-h BASE    { mirror-8 BASE mirror-h_ }

: sprite-1 0x18 0x2C 0x46 0x83 0xEF 0x2C 0x2C 0x3C
: sprite-3 0x18 0x14 0xF2 0x81 0xF3 0xF6 0x1C 0x18
: sprite-2 mirror-v sprite-1
: sprite-4 mirror-h sprite-3