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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v101/c/libe/iefsin.s

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+         ttl       ieee format equivalent (iefsin/iefcos/ieftan)
+***************************************
+* (c) copyright 1981 by motorola inc. *
+***************************************
+ 
+*************************************************
+*            iefsin iefcos ieftan               *
+* ieee format equivalent  sine/cosine/tangent   *
+*                                               *
+*  input:   d7 - ieee format argument (radians) *
+*                                               *
+*  output:  d7 - ieee format function result    *
+*                                               *
+*     all other registers totally transparent   *
+*                                               *
+*        maximum stack used:   54 bytes         *
+*                                               *
+*  condition codes:                             *
+*        z - set if result in d7 is zero        *
+*        n - set if result in d7 is negative    *
+*        c - undefined                          *
+*        v - set if result is nan (not-a-number)*
+*            (input magnitude too large or nan) *
+*        x - undefined                          *
+*                                               *
+*  functions:                                   *
+*             iefsin   -  sine result           *
+*             iefcos   -  cosine result         *
+*             ieftan   -  tangent result        *
+*                                               *
+*  notes:                                       *
+*    1) input values are in radians.            *
+*    2) input arguments larger than two pi      *
+*       suffer reduced precision.  the larger   *
+*       the argument, the smaller the precision.*
+*       excessively large arguments which have  *
+*       less than 5 bits of precision are       *
+*       returned as a nan with the "v" bit set. *
+*    3) the sign of tangents with infinite      *
+*       value is undefined, however we return   *
+*       a positive infinity.                    *
+*    4) spot checks show relative errors bounded*
+*       by 4 x 10**-7 but for arguments close to*
+*       pi/2 intervals where 10**-5 is seen.    *
+*                                               *
+*************************************************
+         page
+iefsin   idnt  1,1 ieee format equivalent sine/cosine/tangent
+ 
+         opt       pcs
+ 
+         section   9
+ 
+         xdef      iefsin,iefcos,ieftan     entry points
+ 
+         xref      ffpsin,ffpcos,ffptan  ffp transcendentals
+         xref      iefsop          single operand front-ender
+         xref      ieftieee        back-end convert back to ieee format
+         xref      iefrtnan        back-end return ieee nan routine
+         xref      ffpcpyrt            copyright stub
+ 
+vbit     equ       $0002     condition code register "v" bit mask
+ffpsign  equ.b     $80       sign in fast floating point value
+ 
+***********************
+* tangent entry point *
+***********************
+ieftan   bsr       iefsop    parse the operand
+         bra.s     ieftnrm   +0 branch not infinity or nan
+         bra       iefrtnan  +2 return nan for infinity
+ 
+* perform tangent function with normalized number
+ieftnrm  bsr       ffptan    find tangent
+         bra.s     iefcmn    enter common exit code
+ 
+**********************
+* cosine entry point *
+**********************
+iefcos   bsr       iefsop    parse the operand
+         bra.s     iefcnrm   +0 branch not infinity or nan
+         bra       iefrtnan  +2 return nan for infinity
+ 
+* perform cosine function with normalized number
+iefcnrm  bsr       ffpcos    find cosine
+         bra.s     iefcmn    enter common exit code
+ 
+********************
+* sine entry point *
+********************
+iefsin   bsr       iefsop    parse the operand
+         bra.s     iefsnrm   +0 branch not infinity or nan
+         bra       iefrtnan  +2 return nan for infinity
+ 
+* perform sine function with normalized number
+iefsnrm  bsr       ffpsin    find sine
+iefcmn   bvc       ieftieee  return if had enough precision
+* overflow can mean true infinity result or not enough precision
+* we can test for not enough precision by checking for largest possible value
+         move.l    d7,d5     copy over ffp format result
+         or.b      #ffpsign,d5 set sign bit to a one
+         sub.l     #1,d5     test for all one bits
+         bne       iefrtnan  no, not enough precision, return a nan
+         tst.b     d7        reset ccr as it was
+         or.b      #vbit,ccr  and show overflow occured
+         bra       ieftieee  restore with infinity of proper sign
+ 
+         end