bni8086.asm

vc环境下的pgp源码

;;; Assembly primitives for bignum library, 80x86 family.
;;;
;;; $Id: bni8086.asm,v 1.2 1997/05/09 20:19:38 lloyd Exp $
;;;
;;; Several primitives are included here.  Only bniMulAdd1 is *really*
;;; critical, but once that's written, bniMul1 and bniSub1 are quite
;;; easy to write as well, so they are included here as well.
;;; bniDiv21 and bniModQ are so easy to write that they're included, too.
;;;
;;; All functions here are for large code, large data.
;;; All use standard "cdecl" calling convention: arguments pushed on the
;;; stack (ss:sp) right to left (the leftmost agrument at the lowest address)
;;; and popped by the caller, return values in ax or dx:ax, and register
;;; usage as follows:
;;;
;;; Callee-save (preserved by callee if needed):
;;;	ss, esp, cs, eip, ds, esi, edi, ebp, high PGPByte of FLAGS except DF,
;;;	all other registers (CRx, DRx, TRx, IDT, GDT, LDT, TR, etc.).
;;; Caller-save (may be corrupted by callee):
;;;	es, eax, ebx, ecx, edx, low PGPByte of flags (SF, ZF, AF, PF, CF)
;;;
;;; The direction flag (DF) is either preserved or cleared.
;;; I'm not sure what the calling convention is for fs and gs.  This
;;; code never alters them.

;; Not all of this code has to be '386 code, but STUPID FUCKING MASM (5.0)
;; gives an error if you change in the middle of a segment.  Rather than
;; fight the thing, just enable '386 instructions everywhere.  (And lose
;; the error checking.)
.386

_TEXT   segment para public use16 'CODE' ; 16-PGPByte aligned because '486 cares
	assume  cs:_TEXT

	public  _bniMulN1_16
	public  _bniMulAdd1_16
	public  _bniMulSub1_16
	public	_bniDiv21_16
	public	_bniModQ_16

	public  _bniMulN1_32
	public  _bniMulAdd1_32
	public  _bniMulSub1_32
	public	_bniDiv21_32
	public	_bniModQ_32

	public	_not386


;; Prototype:
;; BNWORD16
;; bniMulAdd_16(BNWORD16 *out, BNWORD16 *in, unsigned len, BNWORD16 k)
;;
;; Multiply len words of "in" by k and add to len words of "out";
;; return the len+1st word of carry.  All pointers are to the least-
;; significant ends of the appropriate arrays.  len is guaraneed > 0.
;;
;; This 16-bit code is optimized for an 8086/80286.  It will not be run
;; on 32-bit processors except for debugging during development.
;;
;; NOTE that it may be possible to assume that the direction flag is clear
;; on entry; this would avoid the need for the cld instructions.  Hoewever,
;; the Microsoft C libraries require that the direction flag be clear.
;; Thus, bniModQ_16 clears it before returning.
;;
;; Stack frame:
;; +--------+ bp+18
;; |   k    |
;; +--------+ bp+16
;; |  len   |
;; +--------+ bp+14
;; |        |
;; +-  in  -+
;; |        |
;; +--------+ bp+10
;; |        |
;; +- out  -+
;; |        |
;; +--------+ bp+6
;; |        |
;; +-return-+
;; |        |
;; +--------+ bp+2
;; | old bp |
;; +--------+ bp
;;
;; Register usage for bniMul1_16:
;; ds:[si]	in
;; es:[di]	out
;; bp		k
;; cx		loop counter (len/4)
;; dx,ax	high,low parts of product
;; bx		carry from previous multiply iteration
;;
;; Register usage for bniMulAdd1_16 and bniMulSub1_16:
;; ds:[si]	in
;; es:[bx+si]	out
;; bp		k
;; cx		loop counter (len/4)
;; dx,ax	high,low parts of product
;; di		carry from previous multiply iteration
;;
;; The reson for the difference is that straight mul can use stosw, but
;; the multiply and add or multiply and subtract add the result in, so
;; they have to reference es:[di] to add it in.
;;
;; The options are either "add ax,es:[di]; stosw" or "add es:[di],ax;
;; add di,2"; both take 10 cycles on an 80286, 27 on an 8086 and 35 on
;; an 8088 although the former is preferred since it's one PGPByte smaller.
;; However, using [bx+si] is even faster; "add es:[bx+si],ax" takes
;; 7 cycles on an 80286, 25 on an 8086 and 33 on an 8088, as well as
;; being the smallest.  (Of course, stosw, at 3 on an 80286, 11 on an
;; 8086 amd 15 on an 8088 wins easily in the straight multiply case over
;; mov es:[bx+si],ax, which takes 3/18/22 cycles and is larger to boot.)
;;
;; Most of these register assignments are driven by the 8086's instruction
;; set.  The only really practical variation would be to put the multiplier
;; k into bx or di and use bp for carry, but if someone can make a faster
;; Duff's device using a lookup table, bx and di are useful because indexing
;; off them is more flexible than bp.
;;
;; Overview of code:
;;
;; len is guaranteed to be at least 1, so do the first multiply (with no
;; carry in) unconditionally.  Then go to a min loop unrolled 4 times,
;; jumping into the middle using a variant of Duff's device.
;;
;; The loop is constructed using the loop instruction, which does
;; "} while (--cnt)".  This means that we have to divide the count
;; by 4, and increment it so it doesn't start at 0.  To gain a little
;; bit more efficiency, we actually increment the count by 2, so the
;; minimum possible value is 3, which will be shifted down to produce 0.
;; usually in Duff's device, if the number of iterations is a multiple
;; of the unrolling factor, you branch to just before the loop conditional
;; and let it handle the case of 0.  Here, we have a special test for 0
;; at the head of the loop and fall through into the top of the loop
;; if it passes.
;;
;; Basically, with STEP being a multiply step, it's:
;;
;; 	STEP;
;;	count += 2;
;;	mod4 = count % 4;
;;	count /= 4;
;;	switch(mod4) {
;;	  case 3:
;;		if (count) {
;;	  		do {
;;				STEP;
;;	  case 2:
;;				STEP;
;;	  case 1:
;;				STEP;
;;	  case 0:
;;				STEP;
;;			} while (--count);
;;		}
;;	}
;;
;; The switch() is actually done by two levels of branch instructions
;; rather than a lookup table.

_bniMulN1_16	proc	far

	push	bp
	mov	bp,sp
	push	ds
	push	si
	push	di
	cld

	les	di,[bp+6]	; out
	lds	si,[bp+10]	; in
	mov	cx,[bp+14]	; len
	mov     bp,[bp+16]	; k

;; First multiply step has no carry in
	lodsw
	mul	bp
	stosw

;; The switch() for Duff's device starts here
;; Note: this *is* faster than a jump table for an 8086 and '286.
;; 8086:  jump table: 44 cycles; this: 27/29/31/41
;; 80286: jump table: 25 cycles; this: 17/17/20/22
	shr	cx,1
	jc	SHORT m16_odd

	inc	cx
	shr	cx,1
	jc	SHORT m16_case2
	jmp	SHORT m16_case0

	nop			; To align loop
m16_odd:
	inc	cx
	shr	cx,1
	jnc	SHORT m16_case1
	jz	SHORT m16_done	; Avoid entire loop in this case

m16_loop:
	lodsw
	mov	bx,dx		; Remember carry for later
	mul	bp
	add	ax,bx		; Add carry in from previous word
	adc	dx,0
	stosw
m16_case2:
	lodsw
	mov	bx,dx		; Remember carry for later
	mul	bp
	add	ax,bx		; Add carry in from previous word
	adc	dx,0
	stosw
m16_case1:
	lodsw
	mov	bx,dx		; Remember carry for later
	mul	bp
	add	ax,bx		; Add carry in from previous word
	adc	dx,0
	stosw
m16_case0:
	lodsw
	mov	bx,dx		; Remember carry for later
	mul	bp
	add	ax,bx		; Add carry in from previous word
	adc	dx,0
	stosw

	loop	m16_loop

m16_done:
	mov	ax,dx
	stosw			; Store last word
	pop	di
	pop	si
	pop	ds
	pop	bp
	ret

_bniMulN1_16	endp


	align	2
_bniMulAdd1_16	proc	far

	push	bp
	mov	bp,sp
	push	ds
	push	si
	push	di
	cld

	les	bx,[bp+6]	; out
	lds	si,[bp+10]	; in
	mov	cx,[bp+14]	; len
	mov     bp,[bp+16]	; k

;; First multiply step has no carry in
	lodsw
	mul	bp
	add	es:[bx],ax	; This time, store in [bx] directly
	adc	dx,0
	sub	bx,si		; Prepare to use [bx+si].

;; The switch() for Duff's device starts here
;; Note: this *is* faster than a jump table for an 8086 and '286.
;; 8086:  jump table: 44 cycles; this: 27/29/31/41
;; 80286: jump table: 25 cycles; this: 17/17/20/22
	shr	cx,1
	jc	SHORT ma16_odd

	inc	cx
	shr	cx,1
	jc	SHORT ma16_case2
	jmp	SHORT ma16_case0

ma16_odd:
	inc	cx
	shr	cx,1
	jnc	SHORT ma16_case1
	jz	SHORT ma16_done	; Avoid entire loop in this case

ma16_loop:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	add	es:[bx+si],ax
	adc	dx,0
ma16_case2:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	add	es:[bx+si],ax
	adc	dx,0
ma16_case1:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	add	es:[bx+si],ax
	adc	dx,0
ma16_case0:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	add	es:[bx+si],ax
	adc	dx,0

	loop	ma16_loop

ma16_done:
	mov	ax,dx
	pop	di
	pop	si
	pop	ds
	pop	bp
	ret

_bniMulAdd1_16	endp

	align	2
_bniMulSub1_16	proc	far

	push	bp
	mov	bp,sp
	push	ds
	push	si
	push	di
	cld

	les	bx,[bp+6]	; out
	lds	si,[bp+10]	; in
	mov	cx,[bp+14]	; len
	mov     bp,[bp+16]	; k

;; First multiply step has no carry in
	lodsw
	mul	bp
	sub	es:[bx],ax	; This time, store in [bx] directly
	adc	dx,0
	sub	bx,si		; Prepare to use [bx+si].

;; The switch() for Duff's device starts here
;; Note: this *is* faster than a jump table for an 8086 and '286.
;; 8086:  jump table: 44 cycles; this: 27/29/31/41
;; 80286: jump table: 25 cycles; this: 17/17/20/22
	shr	cx,1
	jc	SHORT ms16_odd

	inc	cx
	shr	cx,1
	jc	SHORT ms16_case2
	jmp	SHORT ms16_case0

ms16_odd:
	inc	cx
	shr	cx,1
	jnc	SHORT ms16_case1
	jz	SHORT ms16_done	; Avoid entire loop in this case

ms16_loop:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	sub	es:[bx+si],ax
	adc	dx,0
ms16_case2:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	sub	es:[bx+si],ax
	adc	dx,0
ms16_case1:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	sub	es:[bx+si],ax
	adc	dx,0
ms16_case0:
	lodsw
	mov	di,dx		; Remember carry for later
	mul	bp
	add	ax,di		; Add carry in from previous word
	adc	dx,0
	sub	es:[bx+si],ax
	adc	dx,0

	loop	ms16_loop

ms16_done:
	mov	ax,dx
	pop	di
	pop	si
	pop	ds
	pop	bp
	ret

_bniMulSub1_16	endp

;; Two-word by one-word divide.  Stores quotient, returns remainder.
;; BNWORD16 bniDiv21_16(BNWORD16 *q, BNWORD16 nh, BNWORD16 nl, BNWORD16 d)
;;                      4            8            10           12
	align	2
_bniDiv21_16	proc	far
	mov	cx,bp		; bp NOT pushed; note change in offsets
	mov	bp,sp
	mov	dx,[bp+8]
	mov	ax,[bp+10]
	div	WORD PTR [bp+12]
	les	bx,[bp+4]
	mov	es:[bx],ax
	mov	ax,dx
	mov	bp,cx
	ret

	nop		; To align loop in bniModQ properly

_bniDiv21_16	endp

;; Multi-word by one-word remainder.
;; BNWORD16 bniModQ_16(BNWORD16 *q, unsigned len, unsigned d)
;;                     6            10            12
_bniModQ_16	proc	far
	push	bp
	mov	bp,sp
	push	ds
	mov	bx,si
	mov	cx,10[bp]	; load len
	lds	si,6[bp]	; load q
	std			; loop MSW to LSW
	add	si,cx
	mov	bp,12[bp]	; load d
	add	si,cx
	xor	dx,dx		; Set up for first divide
	sub	si,2		; Adjust pointer to point to MSW

	lodsw			; Load first word

	cmp	ax,bp		; See if we can skip first divide
	jnc	SHORT modq16_inner	; No such luck
	mov	dx,ax		; Yes!  Modulus > input, so remainder = input
	dec	cx		; Do loop
	jz	SHORT modq16_done

modq16_loop:
	lodsw
modq16_inner:
	div	bp
	loop	modq16_loop
modq16_done:
	pop	ds
	mov	ax,dx	; Return remainder
	pop	bp
	mov	si,bx
	cld		; Microsoft C's libraries assume this
	ret

_bniModQ_16	endp


;; Similar, but using 32-bit operations.
;;
;; The differences are that the switch() in Duff's device is done using
;; a jump table, and lods is not used because it's slower than load and
;; increment.  The pointers are only updated once per loop; offset
;; addressing modes are used, since they're no slower.  [di] is used
;; instead of [bx+si] because the extra increment of di take only one
;; cycle per loop a '486, while [bx+si] takes one extra cycle per multiply.
;;
;; The register assignments are also slightly different:
;;
;; es:[si]	in
;; ds:[di]	out
;; ecx		k
;; bp		loop counter (len/4)
;; edx,eax	high,low parts of product
;; ebx		carry word from previous multiply iteration
;;
;; The use of bp for a loop counter lets all the 32-bit values go
;; in caller-save registers, so there's no need to do any 32-bit
;; saves and restores.  Using ds:di for the destination saves one
;; segment override in the bniMulN1_32 code, since there's one more
;; store to [di] than load from es:[si].
;;
;; Given the number of 32-bit references that this code uses, optimizing
;; it for the Pentium is interesting, because the Pentium has a very
;; inefficient implementation of prefix bytes.  Each prefix PGPByte, with
;; the exception of 0x0f *>> on conditional branch instructions ONLY <<*
;; is a 1-cycle non-pairiable instruction.  Which has the effect of
;; forcing the instruction it's on into the U pipe.  But this code uses
;; *lots* of prefix bytes, notably the 0x66 operand size override.
;;
;; For example "add [di],eax" is advised against in Intel's optimization
;; papers, because it takes 3 cycles and 2 of them are not pairable.
;; But any longer sequence would have a prefix PGPByte on every instruction,
;; resulting in even more non-pairable cycles.  Also, only two instructions
;; in the multiply kernel can go in the V pipe (the increments of si and
;; di), and they're already there, so the pairable cycles would be wasted.
;;
;; Things would be *quite* different in native 32-bit mode.
;;
;; All instructions that could go in the V pipe that aren't there are
;; marked.
;;
;; The setup code is quite intricately interleaved to get the best possible