mirror of https://github.com/nmlgc/ReC98.git
138 lines
2.2 KiB
NASM
138 lines
2.2 KiB
NASM
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;
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; Description:
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; 四捨五入つき平方根
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; 距離
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;
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; Function:
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; int pascal isqrt( long x ) ;
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; int pascal ihypot( int x, int y ) ;
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;
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; Parameters:
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; long x ... 平方根を求めたい数
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; 0 <= x < 32767.5↑2
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; ( 0 <= x <= (1073709056 = 3FFF8000h) )
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; これ以外ならばオーバーフロー
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; (a↑bはaのb乗の意味)
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;
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; int x,y ... 距離を得たい座標
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;
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; Returns:
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; int .......... 0 〜 32767
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; x が 0 またはオーバーフローならば 0
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;
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; Requiring Resources:
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; CPU: i8086
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;
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; Author:
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; 恋塚昭彦
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;
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; History:
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; 92/ 7/31 Initial
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; 92/ 8/ 1
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; int ihypot( int x, int y ) ;
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func IHYPOT
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push BP
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mov BP,SP
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@@y = (RETSIZE+2)*2
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@@x = (RETSIZE+1)*2
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mov AX,[BP+@@x]
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imul AX
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mov BX,AX
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mov CX,DX
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mov AX,[BP+@@y]
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imul AX
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add BX,AX
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adc CX,DX
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jmp short ISQRT_ROOT
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endfunc
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; int pascal isqrt( long x ) ;
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;
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; 実装:ニュートン法
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;
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func ISQRT
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push BP
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mov BP,SP
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@@hi = (RETSIZE+2)*2
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@@lo = (RETSIZE+1)*2
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mov BX,[BP+@@lo]
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mov CX,[BP+@@hi]
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ISQRT_ROOT:
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xor AX,AX ; return code = 0
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mov DX,BX
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or DX,CX
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jz short @@RETURN ; x = 0 なら return 0
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cmp CX,03FFFh ; 0〜3FFF8000hでなければ OverFlow! return 0
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ja short @@RETURN
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jne short @@GO
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cmp BX,08000h
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ja short @@RETURN
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@@GO:
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push SI
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shl BX,1 ; CX:BX = x
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rcl CX,1
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shl BX,1
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rcl CX,1 ; x *= 4 ;
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or CX,CX
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if 0
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mov SI,0FFFFh
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jnz short @@LLOOP
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mov SI,8 ; SI: y, BP: lasty
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else
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jz short @@BXLOOPS
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mov SI,1 ; 8000h rol 1
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mov AX,3 ; 0c000h rol 2
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@@CXLOOP:
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ror SI,1
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ror AX,1
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ror AX,1
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test CX,AX
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jz short @@CXLOOP
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or AX,AX
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jns short @@LLOOP
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mov SI,0FFFFh ; 最上位bitが立っている場合は overflowを
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jmp short @@LLOOP ; 防ぐため特例として 0FFFFhを初期値にする
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@@BXLOOPS:
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mov SI,100h ; 80h rol 1
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mov AX,3 ; 0c000h rol 2
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@@BXLOOP:
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ror SI,1
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ror AX,1
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ror AX,1
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test BX,AX
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jz short @@BXLOOP
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; jmp short LLOOP
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endif
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@@LLOOP:
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mov BP,SI ; lasty = y
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mov AX,BX
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mov DX,CX
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div SI
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add SI,AX
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rcr SI,1 ; y = ((unsigned long)x / y + y)/ 2 ;
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cmp SI,AX
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je short @@LEXIT
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cmp SI,BP
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jne short @@LLOOP ; if ( y != lasty ) goto LLOOP ;
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@@LEXIT:
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xor AX,AX
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shr SI,1
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adc AX,SI ; lasty = y & 1 ; return y / 2 + lasty ;
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pop SI
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@@RETURN:
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pop BP
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ret 4
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endfunc
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