コピペ: Untitled

形式

Asm

投稿日時

2021-04-12 11:01

公開期間

無期限

 ;; Copyright 2021 AlaskanEmily
 ;; 
 ;; Permission to use, copy, modify, and/or distribute this software for any
 ;; purpose with or without fee is hereby granted, provided that the above
 ;; copyright notice and this permission notice appear in all copies.
 ;; 
 ;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 ;; AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 ;; IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 ;; ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 ;; LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 ;; CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 ;; SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 ;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 ;; CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 ;; ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 ;; POSSIBILITY OF SUCH DAMAGE.
 
 ; ASM implementation of this C routine:
 ; unsigned interpolate(uint8_t t, uint8_t a, uint8_t b){
 ;   uint8_t value, diff, dx;
 ;   if(a > b){
 ;       value = a;
 ;       a = b;
 ;       b = value;
 ;       t = 255 - t;
 ;   }
 ;   diff = b - a;
 ;   value = a;
 ;   do{
 ;       dx = diff & 1;
 ;       diff >>= 1;
 ;       if(t & 0x80)
 ;           value += diff + dx;
 ;   }while(t <<= 1);
 ;   return value;
 ; }
 ; The extra offset of dx here is a very rough form of rounding.
 ; If you do not include this, then the results will be about 1/16th too low.
 
 ; Calculates the interpolation at a (0 to 255) of b to c
 ; Returns in a.
 interpolate:
     push de
     ld d, a ; Save the T-value in d
     
     ; Swap the interpolation range and T value if necessary
     ld a, c
     sub b
     jrnc @$interpolate_inner
     ; Swap b and c
     ld e, b
     ld b, c
     ld c, e
     
     ; Negate the T-value
     ld a, 0xFF
     sub d
     ld d, a
 $interpolate_inner:
     
     ld a, c
     sub b
     ld e, a
     ; e has the difference now.
     ld a, b
 $interpolate_bit:
     ; srl will set the carry bit, and bit doesn't modify it.
     ; This lets us use adc rather than add plus an inc and a jump below.
     srl e
     bit7 d
     jrz @.no_add
     adc e
 .no_add:
     sla d
     jrnz @$interpolate_bit
     pop de
     ret