;This section performs the 4 sub-multiplies to form
;  the partials to be added later in self-mod code.
;Addresses like "x1y0l+1" refer to low(x1*y0) stored
;  to the argument of a later "adc #{value}"
;mult8_set_mier_snippet {multiplier}
;mult8_snippet {multiplicand}, {low result}, {high result}
+mult8_set_mier_snippet x1          ;17
+mult8_snippet y0, x1y0l+1, x1y0h+1 ;35
+mult8_snippet y1, x1y1l+1, z3      ;32
+mult8_set_mier_snippet x0          ;17
+mult8_snippet "Y", x0y1l+1, "X"    ;28
+mult8_snippet y0, z0, "A"          ;28
;results in X=x0y1h and A=x0y0h
;multiply part total: 149-165, average 157
;z3           z2           z1
                           clc
                     x0y1l adc #0 ;x0y0h + x0y1l
                           tay ;6
              txa
        x1y0h adc #0 ;x0y1h + x1y0h
              tax
              bcc + ;9
inc z3
clc ;(+6) taken 7% of the time
                         + tya
                     x1y0l adc #0 ;+ x1y0l
                           sta z1 ;7
              txa
        x1y1l adc #0 ;+ x1y1l
              bcc done ;7
inc z3 ;(+4) taken 42% of the time

               y1    y0
            x  x1    x0
               --------
            x0y0h x0y0l
      x0y1h x0y1l
      x1y0h x1y0l
x1y1h x1y1l
-----------------------
   z3    z2    z1    z0

!macro mult8_set_mier_snippet .mier {
;set multiplier as mier
;mier can be m/A
;requires .p_.sqr* and .p_.neg.sqr* pointers,
;(mathlib.p_sqr_lo, mathlib.p_neg_sqr_lo, mathlib.p_sqr_hi, mathlib.p_neg_sqr_hi)
;uses these macros from mathlib_util_macros.asm:
;reset_cycles, add_cycles_const
  !if .mier = "X" or .mier = "Y" {
    !error "multlib: mult8_snippet: mier must be m/A, not ", .mier
  } 
  +reset_cycles
  !if .mier != "A" {
    lda .mier
    !if .mier<$100 {
        +add_cycles_const 3
      } else {
        +add_cycles_const 4
      }
  }
  sta mathlib.p_sqr_lo ;3
  sta mathlib.p_sqr_hi ;3
  eor #$ff ;2
  sta mathlib.p_neg_sqr_lo ;3
  sta mathlib.p_neg_sqr_hi ;3; 3+3+3+2+3+3 = 17 cycles
  +add_cycles_const 14
}

mier = x1
(x1) * y0 -> x1y0l, x1y0h
(x1) * y1 -> x1y1l, z3
mier = x0
(x0) * (y1) -> x0y1l, X
(x0) * y0 -> z0, A