mirror of
https://gitlab.com/freepascal.org/fpc/source.git
synced 2025-04-11 18:08:15 +02:00
+ added 32-bit asm optimized division helpers for i8086 by Max Nazhalov
git-svn-id: trunk@26512 -
This commit is contained in:
nickysn
parent
78e726b34f
commit
4a107dcfa6
@ -72,3 +72,198 @@ begin
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HandleErrorAddrFrameInd(215,get_pc_addr,get_frame);
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end;
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{$define FPC_SYSTEM_HAS_DIV_DWORD}
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function fpc_div_dword( n, z: dword ): dword; [public, alias:'FPC_DIV_DWORD']; compilerproc;
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begin
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{ routine contributed by Max Nazhalov }
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result := 0;
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if n=0 then
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HandleErrorAddrFrameInd(200,get_pc_addr,get_frame);
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asm
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mov ax,word [z]
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mov dx,word [z+2]
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mov bx,word [n]
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mov cx,word [n+2]
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// check for underflow: z<n
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mov si,dx
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cmp ax,bx
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sbb si,cx
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jc @@3
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// select one of 3 trivial cases
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test cx,cx
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jnz @@1
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cmp dx,bx
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jnc @@0
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// (i) single division: n<=0xFFFF, z<=(n<<16)-1
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div bx
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mov word [result],ax
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jmp @@3
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@@0: // (ii) two divisions: n<=0xFFFF, z>(n<<16)-1
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// q1 := [0:z1] div n; r := [0:z1] mod n;
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// q0 := [r:z0] div n;
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xchg ax,cx
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xchg ax,dx
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{ dx=0, ax=z1, cx=z0 }
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div bx
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xchg ax,cx
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{ dx=r, ax=z0, cx=q1 }
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div bx
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mov word [result],ax
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mov word [result+2],cx
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jmp @@3
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@@1: // (iii) long divisor: n>=0x10000 (hence q<=0xFFFF)
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// Special case of the generic "schoolbook" division [see e.g. Knuth]:
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// 1. normalize divisor: [n1:n0] := n<<m, so that 0x8000<=n1<=0xFFFF
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// n>=0x10000 -> m<=15
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// 2. adjust divident accordingly: [z2:z1:z0] := z<<m
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// m<=15 -> z2<=0x7FFF
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// implementation: instead do >> dropping n0 and z0
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mov si,bx // save n0
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mov di,cx // save n1
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test ch,ch
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jz @@2
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mov bl,bh
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mov bh,cl
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mov cl,ch
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mov al,ah
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mov ah,dl
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mov dl,dh
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xor dh,dh
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@@2: // repeat >> 1..8 times resulting in [dx:ax]=[z2:z1] and bx=n1
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shr cl,1
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rcr bx,1
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shr dx,1
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rcr ax,1
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test cl,cl
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jnz @@2
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// 3. estimate quotient: q_hat := [z2:z1]/n1
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// Division never overflows since z2<=0x7FFF and n1>0x7FFF
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div bx
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// 4. multiply & subtract calculating remainder:
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// r := z-n*q_hat (z and n are original)
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// 5. adjust quotient: while (r<0) do { q_hat-=1; r+=n };
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// theoretically, 0..2 iterations are required [see e.g. Knuth];
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// in practice, with such initial data, at most one iteration
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// is needed (no disproof has been found yet; and if it will
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// ever be found -- it also should raise doubts about the i386
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// fpc_div_qword helper again; see FPC mantis #23963)
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mov cx,ax // save q_hat
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mul si
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mov bx,ax
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mov si,dx
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mov ax,cx
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mul di
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xor di,di
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add ax,si
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adc dx,di // [dx:ax:bx] := n*q_hat; di=0
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mov si,word [z]
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sub si,bx
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mov si,word [z+2]
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sbb si,ax
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sbb di,dx
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sbb cx,0
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// 6. done: q := [0:cx]
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mov word [result],cx
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@@3:
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end;
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end;
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{$define FPC_SYSTEM_HAS_MOD_DWORD}
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function fpc_mod_dword( n, z: dword ): dword; [public, alias:'FPC_MOD_DWORD']; compilerproc;
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begin
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{ routine contributed by Max Nazhalov }
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result := z;
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if n=0 then
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HandleErrorAddrFrameInd(200,get_pc_addr,get_frame);
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asm
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mov ax,word [z]
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mov dx,word [z+2]
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mov bx,word [n]
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mov cx,word [n+2]
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// check for underflow: z<n
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mov si,dx
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cmp ax,bx
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sbb si,cx
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jc @@4
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// select one of 3 trivial cases
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test cx,cx
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jnz @@1
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cmp dx,bx
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jnc @@0
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// (i) single division: n<=0xFFFF, z<=(n<<16)-1
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div bx
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jmp @@3 // r=cx:dx (cx=0)
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@@0: // (ii) two divisions: n<=0xFFFF, z>(n<<16)-1
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// q1 := [0:z1] div n; r := [0:z1] mod n;
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// q0 := [r:z0] div n; r := [r:z0] mod n;
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xchg ax,cx
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xchg ax,dx
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{ dx=0, ax=z1, cx=z0 }
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div bx
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mov ax,cx
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xor cx,cx
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{ dx=r, ax=z0, cx=0 }
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div bx
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jmp @@3 // r=cx:dx (cx=0)
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@@1: // (iii) long divisor: n>=0x10000 (hence q<=0xFFFF)
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// Special case of the generic "schoolbook" division [see e.g. Knuth]:
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// 1. normalize divisor: [n1:n0] := n<<m, so that 0x8000<=n1<=0xFFFF
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// n>=0x10000 -> m<=15
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// 2. adjust divident accordingly: [z2:z1:z0] := z<<m
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// m<=15 -> z2<=0x7FFF
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// implementation: instead do >> dropping n0 and z0
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mov si,bx // save n0
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mov di,cx // save n1
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test ch,ch
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jz @@2
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mov bl,bh
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mov bh,cl
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mov cl,ch
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mov al,ah
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mov ah,dl
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mov dl,dh
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xor dh,dh
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@@2: // repeat >> 1..8 times resulting in [dx:ax]=[z2:z1] and bx=n1
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shr cl,1
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rcr bx,1
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shr dx,1
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rcr ax,1
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test cl,cl
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jnz @@2
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// 3. estimate quotient: q_hat := [z2:z1]/n1
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// Division never overflows since z2<=0x7FFF and n1>0x7FFF
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div bx
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// 4. multiply & subtract calculating remainder:
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// r := z-n*q_hat (z and n are original)
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// 5. adjust quotient: while (r<0) do { q_hat-=1; r+=n };
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// theoretically, 0..2 iterations are required [see e.g. Knuth];
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// in practice, with such initial data, at most one iteration
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// is needed (no disproof has been found yet; and if it will
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// ever be found -- it also should raise doubts about the i386
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// fpc_div_qword helper again; see FPC mantis #23963)
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mov cx,ax // save q_hat
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mul si
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mov bx,ax
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mov si,dx
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mov ax,cx
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mul di
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xor di,di
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add ax,si
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adc dx,di // [dx:ax:bx] := n*q_hat; di=0
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mov si,word [z]
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mov cx,word [z+2]
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sub si,bx
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sbb cx,ax
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sbb di,dx
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mov dx,si
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jnc @@3
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add dx,word [n]
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adc cx,word [n+2]
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@@3: // done: r=cx:dx
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mov word [result],dx
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mov word [result+2],cx
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@@4:
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end;
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end;
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