source: rtems/c/src/lib/libcpu/m68k/m68040/fpsp/binstr.s @ 1d320bac

//
//      binstr.sa 3.3 12/19/90
//
//
//      Description: Converts a 64-bit binary integer to bcd.
//
//      Input: 64-bit binary integer in d2:d3, desired length (LEN) in
//          d0, and a  pointer to start in memory for bcd characters
//          in d0. (This pointer must point to byte 4 of the first
//          lword of the packed decimal memory string.)
//
//      Output: LEN bcd digits representing the 64-bit integer.
//
//      Algorithm:
//              The 64-bit binary is assumed to have a decimal point before
//              bit 63.  The fraction is multiplied by 10 using a mul by 2
//              shift and a mul by 8 shift.  The bits shifted out of the
//              msb form a decimal digit.  This process is iterated until
//              LEN digits are formed.
//
//      A1. Init d7 to 1.  D7 is the byte digit counter, and if 1, the
//              digit formed will be assumed the least significant.  This is
//              to force the first byte formed to have a 0 in the upper 4 bits.
//
//      A2. Beginning of the loop:
//              Copy the fraction in d2:d3 to d4:d5.
//
//      A3. Multiply the fraction in d2:d3 by 8 using bit-field
//              extracts and shifts.  The three msbs from d2 will go into
//              d1.
//
//      A4. Multiply the fraction in d4:d5 by 2 using shifts.  The msb
//              will be collected by the carry.
//
//      A5. Add using the carry the 64-bit quantities in d2:d3 and d4:d5
//              into d2:d3.  D1 will contain the bcd digit formed.
//
//      A6. Test d7.  If zero, the digit formed is the ms digit.  If non-
//              zero, it is the ls digit.  Put the digit in its place in the
//              upper word of d0.  If it is the ls digit, write the word
//              from d0 to memory.
//
//      A7. Decrement d6 (LEN counter) and repeat the loop until zero.
//
//      Implementation Notes:
//
//      The registers are used as follows:
//
//              d0: LEN counter
//              d1: temp used to form the digit
//              d2: upper 32-bits of fraction for mul by 8
//              d3: lower 32-bits of fraction for mul by 8
//              d4: upper 32-bits of fraction for mul by 2
//              d5: lower 32-bits of fraction for mul by 2
//              d6: temp for bit-field extracts
//              d7: byte digit formation word;digit count {0,1}
//              a0: pointer into memory for packed bcd string formation
//

//              Copyright (C) Motorola, Inc. 1990
//                      All Rights Reserved
//
//      THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
//      The copyright notice above does not evidence any  
//      actual or intended publication of such source code.

//BINSTR    idnt    2,1 | Motorola 040 Floating Point Software Package

        |section        8

#include "fpsp.defs"

        .global binstr
binstr:
        moveml  %d0-%d7,-(%a7)
//
// A1: Init d7
//
        moveql  #1,%d7                  //init d7 for second digit
        subql   #1,%d0                  //for dbf d0 would have LEN+1 passes
//
// A2. Copy d2:d3 to d4:d5.  Start loop.
//
loop:
        movel   %d2,%d4                 //copy the fraction before muls
        movel   %d3,%d5                 //to d4:d5
//
// A3. Multiply d2:d3 by 8; extract msbs into d1.
//
        bfextu  %d2{#0:#3},%d1          //copy 3 msbs of d2 into d1
        asll    #3,%d2                  //shift d2 left by 3 places
        bfextu  %d3{#0:#3},%d6          //copy 3 msbs of d3 into d6
        asll    #3,%d3                  //shift d3 left by 3 places
        orl     %d6,%d2                 //or in msbs from d3 into d2
//
// A4. Multiply d4:d5 by 2; add carry out to d1.
//
        asll    #1,%d5                  //mul d5 by 2
        roxll   #1,%d4                  //mul d4 by 2
        swap    %d6                     //put 0 in d6 lower word
        addxw   %d6,%d1                 //add in extend from mul by 2
//
// A5. Add mul by 8 to mul by 2.  D1 contains the digit formed.
//
        addl    %d5,%d3                 //add lower 32 bits
        nop                             //ERRATA ; FIX #13 (Rev. 1.2 6/6/90)
        addxl   %d4,%d2                 //add with extend upper 32 bits
        nop                             //ERRATA ; FIX #13 (Rev. 1.2 6/6/90)
        addxw   %d6,%d1                 //add in extend from add to d1
        swap    %d6                     //with d6 = 0; put 0 in upper word
//
// A6. Test d7 and branch.
//
        tstw    %d7                     //if zero, store digit & to loop
        beqs    first_d                 //if non-zero, form byte & write
sec_d:
        swap    %d7                     //bring first digit to word d7b
        aslw    #4,%d7                  //first digit in upper 4 bits d7b
        addw    %d1,%d7                 //add in ls digit to d7b
        moveb   %d7,(%a0)+              //store d7b byte in memory
        swap    %d7                     //put LEN counter in word d7a
        clrw    %d7                     //set d7a to signal no digits done
        dbf     %d0,loop                //do loop some more!
        bras    end_bstr                //finished, so exit
first_d:
        swap    %d7                     //put digit word in d7b
        movew   %d1,%d7                 //put new digit in d7b
        swap    %d7                     //put LEN counter in word d7a
        addqw   #1,%d7                  //set d7a to signal first digit done
        dbf     %d0,loop                //do loop some more!
        swap    %d7                     //put last digit in string
        lslw    #4,%d7                  //move it to upper 4 bits
        moveb   %d7,(%a0)+              //store it in memory string
//
// Clean up and return with result in fp0.
//
end_bstr:
        moveml  (%a7)+,%d0-%d7
        rts
        |end