.file "reg_u_div.S" /* $OpenBSD: reg_u_div.s,v 1.1 1996/08/27 10:33:01 downsj Exp $ */ /* * reg_u_div.S * * Core division routines * * * Copyright (C) 1992,1993,1994 * W. Metzenthen, 22 Parker St, Ormond, Vic 3163, * Australia. E-mail billm@vaxc.cc.monash.edu.au * All rights reserved. * * This copyright notice covers the redistribution and use of the * FPU emulator developed by W. Metzenthen. It covers only its use * in the 386BSD, FreeBSD and NetBSD operating systems. Any other * use is not permitted under this copyright. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must include information specifying * that source code for the emulator is freely available and include * either: * a) an offer to provide the source code for a nominal distribution * fee, or * b) list at least two alternative methods whereby the source * can be obtained, e.g. a publically accessible bulletin board * and an anonymous ftp site from which the software can be * downloaded. * 3. All advertising materials specifically mentioning features or use of * this emulator must acknowledge that it was developed by W. Metzenthen. * 4. The name of W. Metzenthen may not be used to endorse or promote * products derived from this software without specific prior written * permission. * * THIS SOFTWARE IS PROVIDED ``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 * W. METZENTHEN 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. * * * The purpose of this copyright, based upon the Berkeley copyright, is to * ensure that the covered software remains freely available to everyone. * * The software (with necessary differences) is also available, but under * the terms of the GNU copyleft, for the Linux operating system and for * the djgpp ms-dos extender. * * W. Metzenthen June 1994. * * * $FreeBSD: reg_u_div.s,v 1.3 1994/06/10 07:44:57 rich Exp $ * */ /*---------------------------------------------------------------------------+ | Kernel for the division routines. | | | | void reg_u_div(FPU_REG *a, FPU_REG *a, | | FPU_REG *dest, unsigned int control_word) | | | | Does not compute the destination exponent, but does adjust it. | +---------------------------------------------------------------------------*/ #include #include #include #include /* #define dSIGL(x) (x) */ /* #define dSIGH(x) 4(x) */ .data /* Local storage: Result: accum_3:accum_2:accum_1:accum_0 Overflow flag: ovfl_flag */ .align 2,0 accum_3: .long 0 accum_2: .long 0 accum_1: .long 0 accum_0: .long 0 result_1: .long 0 result_2: .long 0 ovfl_flag: .byte 0 .text .align 2,144 .globl _reg_u_div .globl _divide_kernel _reg_u_div: pushl %ebp movl %esp,%ebp pushl %esi pushl %edi pushl %ebx movl PARAM1,%esi /* pointer to num */ movl PARAM2,%ebx /* pointer to denom */ movl PARAM3,%edi /* pointer to answer */ #ifdef DENORM_OPERAND movl EXP(%esi),%eax cmpl EXP_UNDER,%eax jg xOp1_not_denorm call _denormal_operand orl %eax,%eax jnz FPU_Arith_exit xOp1_not_denorm: movl EXP(%ebx),%eax cmpl EXP_UNDER,%eax jg xOp2_not_denorm call _denormal_operand orl %eax,%eax jnz FPU_Arith_exit xOp2_not_denorm: #endif DENORM_OPERAND _divide_kernel: #ifdef PARANOID /* testl $0x80000000, SIGH(%esi) *//* Dividend */ /* je L_bugged */ testl $0x80000000, SIGH(%ebx) /* Divisor*/ je L_bugged #endif PARANOID /* Check if the divisor can be treated as having just 32 bits */ cmpl $0,SIGL(%ebx) jnz L_Full_Division /* Can't do a quick divide */ /* We should be able to zip through the division here */ movl SIGH(%ebx),%ecx /* The divisor */ movl SIGH(%esi),%edx /* Dividend */ movl SIGL(%esi),%eax /* Dividend */ cmpl %ecx,%edx setaeb ovfl_flag /* Keep a record */ jb L_no_adjust subl %ecx,%edx /* Prevent the overflow */ L_no_adjust: /* Divide the 64 bit number by the 32 bit denominator */ divl %ecx movl %eax,result_2 /* Work on the remainder of the first division */ xorl %eax,%eax divl %ecx movl %eax,result_1 /* Work on the remainder of the 64 bit division */ xorl %eax,%eax divl %ecx testb $255,ovfl_flag /* was the num > denom ? */ je L_no_overflow /* Do the shifting here */ /* increase the exponent */ incl EXP(%edi) /* shift the mantissa right one bit */ stc /* To set the ms bit */ rcrl result_2 rcrl result_1 rcrl %eax L_no_overflow: jmp LRound_precision /* Do the rounding as required*/ /*---------------------------------------------------------------------------+ | Divide: Return arg1/arg2 to arg3. | | | | This routine does not use the exponents of arg1 and arg2, but does | | adjust the exponent of arg3. | | | | The maximum returned value is (ignoring exponents) | | .ffffffff ffffffff | | ------------------ = 1.ffffffff fffffffe | | .80000000 00000000 | | and the minimum is | | .80000000 00000000 | | ------------------ = .80000000 00000001 (rounded) | | .ffffffff ffffffff | | | +---------------------------------------------------------------------------*/ L_Full_Division: /* Save extended dividend in local register*/ movl SIGL(%esi),%eax movl %eax,accum_2 movl SIGH(%esi),%eax movl %eax,accum_3 xorl %eax,%eax movl %eax,accum_1 /* zero the extension */ movl %eax,accum_0 /* zero the extension */ movl SIGL(%esi),%eax /* Get the current num */ movl SIGH(%esi),%edx /*----------------------------------------------------------------------*/ /* Initialization done */ /* Do the first 32 bits */ movb $0,ovfl_flag cmpl SIGH(%ebx),%edx /* Test for imminent overflow */ jb LLess_than_1 ja LGreater_than_1 cmpl SIGL(%ebx),%eax jb LLess_than_1 LGreater_than_1: /* The dividend is greater or equal, would cause overflow */ setaeb ovfl_flag /* Keep a record */ subl SIGL(%ebx),%eax sbbl SIGH(%ebx),%edx /* Prevent the overflow */ movl %eax,accum_2 movl %edx,accum_3 LLess_than_1: /* At this point, we have a dividend < divisor, with a record of adjustment in ovfl_flag */ /* We will divide by a number which is too large */ movl SIGH(%ebx),%ecx addl $1,%ecx jnc LFirst_div_not_1 /* here we need to divide by 100000000h, i.e., no division at all.. */ mov %edx,%eax jmp LFirst_div_done LFirst_div_not_1: divl %ecx /* Divide the numerator by the augmented denom ms dw */ LFirst_div_done: movl %eax,result_2 /* Put the result in the answer */ mull SIGH(%ebx) /* mul by the ms dw of the denom */ subl %eax,accum_2 /* Subtract from the num local reg */ sbbl %edx,accum_3 movl result_2,%eax /* Get the result back */ mull SIGL(%ebx) /* now mul the ls dw of the denom */ subl %eax,accum_1 /* Subtract from the num local reg */ sbbl %edx,accum_2 sbbl $0,accum_3 je LDo_2nd_32_bits /* Must check for non-zero result here */ #ifdef PARANOID jb L_bugged_1 #endif PARANOID /* need to subtract another once of the denom */ incl result_2 /* Correct the answer */ movl SIGL(%ebx),%eax movl SIGH(%ebx),%edx subl %eax,accum_1 /* Subtract from the num local reg */ sbbl %edx,accum_2 #ifdef PARANOID sbbl $0,accum_3 jne L_bugged_1 /* Must check for non-zero result here */ #endif PARANOID /*----------------------------------------------------------------------*/ /* Half of the main problem is done, there is just a reduced numerator to handle now */ /* Work with the second 32 bits, accum_0 not used from now on */ LDo_2nd_32_bits: movl accum_2,%edx /* get the reduced num */ movl accum_1,%eax /* need to check for possible subsequent overflow */ cmpl SIGH(%ebx),%edx jb LDo_2nd_div ja LPrevent_2nd_overflow cmpl SIGL(%ebx),%eax jb LDo_2nd_div LPrevent_2nd_overflow: /* The numerator is greater or equal, would cause overflow */ /* prevent overflow */ subl SIGL(%ebx),%eax sbbl SIGH(%ebx),%edx movl %edx,accum_2 movl %eax,accum_1 incl result_2 /* Reflect the subtraction in the answer */ #ifdef PARANOID je L_bugged_2 /* Can't bump the result to 1.0 */ #endif PARANOID LDo_2nd_div: cmpl $0,%ecx /* augmented denom msw*/ jnz LSecond_div_not_1 /* %ecx == 0, we are dividing by 1.0 */ mov %edx,%eax jmp LSecond_div_done LSecond_div_not_1: divl %ecx /* Divide the numerator by the denom ms dw */ LSecond_div_done: movl %eax,result_1 /* Put the result in the answer */ mull SIGH(%ebx) /* mul by the ms dw of the denom */ subl %eax,accum_1 /* Subtract from the num local reg */ sbbl %edx,accum_2 #ifdef PARANOID jc L_bugged_2 #endif PARANOID movl result_1,%eax /* Get the result back */ mull SIGL(%ebx) /* now mul the ls dw of the denom */ subl %eax,accum_0 /* Subtract from the num local reg */ sbbl %edx,accum_1 /* Subtract from the num local reg */ sbbl $0,accum_2 #ifdef PARANOID jc L_bugged_2 #endif PARANOID jz LDo_3rd_32_bits #ifdef PARANOID cmpl $1,accum_2 jne L_bugged_2 #endif PARANOID /* need to subtract another once of the denom */ movl SIGL(%ebx),%eax movl SIGH(%ebx),%edx subl %eax,accum_0 /* Subtract from the num local reg */ sbbl %edx,accum_1 sbbl $0,accum_2 #ifdef PARANOID jc L_bugged_2 jne L_bugged_2 #endif PARANOID addl $1,result_1 /* Correct the answer */ adcl $0,result_2 #ifdef PARANOID jc L_bugged_2 /* Must check for non-zero result here */ #endif PARANOID /*----------------------------------------------------------------------*/ /* The division is essentially finished here, we just need to perform tidying operations. */ /* deal with the 3rd 32 bits */ LDo_3rd_32_bits: movl accum_1,%edx /* get the reduced num */ movl accum_0,%eax /* need to check for possible subsequent overflow */ cmpl SIGH(%ebx),%edx /* denom*/ jb LRound_prep ja LPrevent_3rd_overflow cmpl SIGL(%ebx),%eax /* denom */ jb LRound_prep LPrevent_3rd_overflow: /* prevent overflow */ subl SIGL(%ebx),%eax sbbl SIGH(%ebx),%edx movl %edx,accum_1 movl %eax,accum_0 addl $1,result_1 /* Reflect the subtraction in the answer */ adcl $0,result_2 jne LRound_prep jnc LRound_prep /* This is a tricky spot, there is an overflow of the answer */ movb $255,ovfl_flag /* Overflow -> 1.000 */ LRound_prep: /* Prepare for rounding. // To test for rounding, we just need to compare 2*accum with the // denom. */ movl accum_0,%ecx movl accum_1,%edx movl %ecx,%eax orl %edx,%eax jz LRound_ovfl /* The accumulator contains zero.*/ /* Multiply by 2 */ clc rcll $1,%ecx rcll $1,%edx jc LRound_large /* No need to compare, denom smaller */ subl SIGL(%ebx),%ecx sbbl SIGH(%ebx),%edx jnc LRound_not_small movl $0x70000000,%eax /* Denom was larger */ jmp LRound_ovfl LRound_not_small: jnz LRound_large movl $0x80000000,%eax /* Remainder was exactly 1/2 denom */ jmp LRound_ovfl LRound_large: movl $0xff000000,%eax /* Denom was smaller */ LRound_ovfl: /* We are now ready to deal with rounding, but first we must get the bits properly aligned */ testb $255,ovfl_flag /* was the num > denom ? */ je LRound_precision incl EXP(%edi) /* shift the mantissa right one bit */ stc /* Will set the ms bit */ rcrl result_2 rcrl result_1 rcrl %eax /* Round the result as required */ LRound_precision: decl EXP(%edi) /* binary point between 1st & 2nd bits */ movl %eax,%edx movl result_1,%ebx movl result_2,%eax jmp FPU_round #ifdef PARANOID /* The logic is wrong if we got here */ L_bugged: pushl EX_INTERNAL|0x202 call EXCEPTION pop %ebx jmp L_exit L_bugged_1: pushl EX_INTERNAL|0x203 call EXCEPTION pop %ebx jmp L_exit L_bugged_2: pushl EX_INTERNAL|0x204 call EXCEPTION pop %ebx jmp L_exit L_exit: popl %ebx popl %edi popl %esi leave ret #endif PARANOID