Return to README CVS log

Up to [CSRG BSD Unix] / 43BSDReno / lib / libm / mc68881

Annotation of 43BSDReno/lib/libm/mc68881/README, revision 1.1

1.1     ! root        1: These routines were produced by someone who is not a great authority on
        !             2: floating point, and may not be entirely correct.  Where possible I tested
        !             3: the special cases for routines.
        !             4: 
        !             5: The directory testieee contains test programs for IEEE-format machines.
        !             6: I took a stab at making them work on the vax, but gave up as dealing with
        !             7: exceptions (e.g. underflow, overflow, reserved operand) was just too tedious.
        !             8: 
        !             9: Note: it is possible to build a library with MACHINE=ieee but a couple
        !            10: of warnings:
        !            11: 
        !            12:        Be careful when compiling floor.c.  These routines rely on
        !            13:        certain variables being only double precision.  If these
        !            14:        variables are placed in 68881 registers, they will be extended
        !            15:        precision and the routines will produce incorrect results.
        !            16:        Unless your compiler does its own register allocation, this
        !            17:        is not likely to be a problem as none of the variables in
        !            18:        question are declared "register".  If you are using GCC
        !            19:        you can specify -ffloat-store to avoid this problem.
        !            20: 
        !            21:        The C version of drem() in ieee/support.c appears to compute
        !            22:        the incorrect results for drem(+-1, +-2).  It yields 1 when
        !            23:        it should be -1 and -1 when it should be 1.  "should be" is
        !            24:        based on what the VAX version yields and by cranking through
        !            25:        the formula.
        !            26: 
        !            27: If you do build using MACHINE=ieee and run the tests in testieee you
        !            28: will note that some routines return errors:
        !            29: 
        !            30:        floor/ceil/rint report that they got 0 when expecting -0.
        !            31:        Don't really know which is correct, is floor(-0) == 0 or -0?
        !            32:        For C it shouldn't really matter since 0 is the same as -0
        !            33:        in comparisons.
        !            34: 
        !            35:        scalb(-1, -2100) returns 0 instead of -0.  2 ** -2100 is
        !            36:        effectively 0 but -anything * 0 == -0 according to the 68881.
        !            37:        Similarly for scalb(-pi, 2100).  It returns INF instead
        !            38:        of -INF.  2 ** 2100 is effectively INF but -anything * INF
        !            39:        is -INF.  What is correct?
        !            40: 
        !            41:        drem(+-1, +-2) fails as mentioned above.  This is a real error.
        !            42: 
        !            43: ----
        !            44: Mike Hibler
        !            45: U of Utah CS Dept.
        !            46: [email protected]

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.