/* SPDX-License-Identifier: GPL-2.0 */ .file "reg_u_div.S" /*---------------------------------------------------------------------------+ | reg_u_div.S | | | | Divide one FPU_REG by another and put the result in a destination FPU_REG.| | | | Copyright (C) 1992,1993,1995,1997 | | W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia | | E-mail billm@suburbia.net | | | | | +---------------------------------------------------------------------------*/ /*---------------------------------------------------------------------------+ | Call from C as: | | int FPU_u_div(FPU_REG *a, FPU_REG *b, FPU_REG *dest, | | unsigned int control_word, char *sign) | | | | Does not compute the destination exponent, but does adjust it. | | | | Return value is the tag of the answer, or-ed with FPU_Exception if | | one was raised, or -1 on internal error. | +---------------------------------------------------------------------------*/ #include "exception.h" #include "fpu_emu.h" #include "control_w.h" /* #define dSIGL(x) (x) */ /* #define dSIGH(x) 4(x) */ #ifndef NON_REENTRANT_FPU /* Local storage on the stack: Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 Overflow flag: ovfl_flag */ #define FPU_accum_3 -4(%ebp) #define FPU_accum_2 -8(%ebp) #define FPU_accum_1 -12(%ebp) #define FPU_accum_0 -16(%ebp) #define FPU_result_1 -20(%ebp) #define FPU_result_2 -24(%ebp) #define FPU_ovfl_flag -28(%ebp) #else .data /* Local storage in a static area: Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 Overflow flag: ovfl_flag */ .align 4,0 FPU_accum_3: .long 0 FPU_accum_2: .long 0 FPU_accum_1: .long 0 FPU_accum_0: .long 0 FPU_result_1: .long 0 FPU_result_2: .long 0 FPU_ovfl_flag: .byte 0 #endif /* NON_REENTRANT_FPU */ #define REGA PARAM1 #define REGB PARAM2 #define DEST PARAM3 .text SYM_FUNC_START(FPU_u_div) pushl %ebp movl %esp,%ebp #ifndef NON_REENTRANT_FPU subl $28,%esp #endif /* NON_REENTRANT_FPU */ pushl %esi pushl %edi pushl %ebx movl REGA,%esi movl REGB,%ebx movl DEST,%edi movswl EXP(%esi),%edx movswl EXP(%ebx),%eax subl %eax,%edx addl EXP_BIAS,%edx /* A denormal and a large number can cause an exponent underflow */ cmpl EXP_WAY_UNDER,%edx jg xExp_not_underflow /* Set to a really low value allow correct handling */ movl EXP_WAY_UNDER,%edx xExp_not_underflow: movw %dx,EXP(%edi) #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 FPU_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,FPU_result_2 /* Work on the remainder of the first division */ xorl %eax,%eax divl %ecx movl %eax,FPU_result_1 /* Work on the remainder of the 64 bit division */ xorl %eax,%eax divl %ecx testb $255,FPU_ovfl_flag /* was the num > denom ? */ je L_no_overflow /* Do the shifting here */ /* increase the exponent */ incw EXP(%edi) /* shift the mantissa right one bit */ stc /* To set the ms bit */ rcrl FPU_result_2 rcrl FPU_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,FPU_accum_2 movl SIGH(%esi),%eax movl %eax,FPU_accum_3 xorl %eax,%eax movl %eax,FPU_accum_1 /* zero the extension */ movl %eax,FPU_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,FPU_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 FPU_ovfl_flag /* Keep a record */ subl SIGL(%ebx),%eax sbbl SIGH(%ebx),%edx /* Prevent the overflow */ movl %eax,FPU_accum_2 movl %edx,FPU_accum_3 LLess_than_1: /* At this point, we have a dividend < divisor, with a record of adjustment in FPU_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,FPU_result_2 /* Put the result in the answer */ mull SIGH(%ebx) /* mul by the ms dw of the denom */ subl %eax,FPU_accum_2 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_3 movl FPU_result_2,%eax /* Get the result back */ mull SIGL(%ebx) /* now mul the ls dw of the denom */ subl %eax,FPU_accum_1 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_2 sbbl $0,FPU_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 FPU_result_2 /* Correct the answer */ movl SIGL(%ebx),%eax movl SIGH(%ebx),%edx subl %eax,FPU_accum_1 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_2 #ifdef PARANOID sbbl $0,FPU_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, FPU_accum_0 not used from now on */ LDo_2nd_32_bits: movl FPU_accum_2,%edx /* get the reduced num */ movl FPU_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,FPU_accum_2 movl %eax,FPU_accum_1 incl FPU_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,FPU_result_1 /* Put the result in the answer */ mull SIGH(%ebx) /* mul by the ms dw of the denom */ subl %eax,FPU_accum_1 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_2 #ifdef PARANOID jc L_bugged_2 #endif /* PARANOID */ movl FPU_result_1,%eax /* Get the result back */ mull SIGL(%ebx) /* now mul the ls dw of the denom */ subl %eax,FPU_accum_0 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */ sbbl $0,FPU_accum_2 #ifdef PARANOID jc L_bugged_2 #endif /* PARANOID */ jz LDo_3rd_32_bits #ifdef PARANOID cmpl $1,FPU_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,FPU_accum_0 /* Subtract from the num local reg */ sbbl %edx,FPU_accum_1 sbbl $0,FPU_accum_2 #ifdef PARANOID jc L_bugged_2 jne L_bugged_2 #endif /* PARANOID */ addl $1,FPU_result_1 /* Correct the answer */ adcl $0,FPU_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 FPU_accum_1,%edx /* get the reduced num */ movl FPU_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,FPU_accum_1 movl %eax,FPU_accum_0 addl $1,FPU_result_1 /* Reflect the subtraction in the answer */ adcl $0,FPU_result_2 jne LRound_prep jnc LRound_prep /* This is a tricky spot, there is an overflow of the answer */ movb $255,FPU_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 FPU_accum_0,%ecx movl FPU_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,FPU_ovfl_flag /* was the num > denom ? */ je LRound_precision incw EXP(%edi) /* shift the mantissa right one bit */ stc /* Will set the ms bit */ rcrl FPU_result_2 rcrl FPU_result_1 rcrl %eax /* Round the result as required */ LRound_precision: decw EXP(%edi) /* binary point between 1st & 2nd bits */ movl %eax,%edx movl FPU_result_1,%ebx movl FPU_result_2,%eax jmp fpu_reg_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: movl $-1,%eax popl %ebx popl %edi popl %esi leave RET #endif /* PARANOID */ SYM_FUNC_END(FPU_u_div)