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Annotation of 43BSDTahoe/lib/libc/gen/gen.tahoe/ldexp.s, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1988 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  * This code is derived from software contributed to Berkeley by
        !            18:  * Computer Consoles Inc.
        !            19:  */
        !            20: 
        !            21: #if defined(LIBC_SCCS) && !defined(lint)
        !            22:        .asciz "@(#)ldexp.s     1.3 (Berkeley) 6/27/88"
        !            23: #endif /* LIBC_SCCS and not lint */
        !            24: 
        !            25: /*
        !            26:  * double ldexp (value, exp)
        !            27:  *     double value;
        !            28:  *     int exp;
        !            29:  *
        !            30:  * Ldexp returns value*2**exp, if that result is in range.
        !            31:  * If underflow occurs, it returns zero.  If overflow occurs,
        !            32:  * it returns a value of appropriate sign and largest
        !            33:  * possible magnitude.  In case of either overflow or underflow,
        !            34:  * the external int "errno" is set to ERANGE.  Note that errno is
        !            35:  * not modified if no error occurs, so if you intend to test it
        !            36:  * after you use ldexp, you had better set it to something
        !            37:  * other than ERANGE first (zero is a reasonable value to use).
        !            38:  *
        !            39:  * Constants
        !            40:  */
        !            41: #include <errno.h>
        !            42: #include <tahoemath/fp.h>
        !            43: 
        !            44: #include "DEFS.h"
        !            45: 
        !            46: ENTRY(ldexp, 0)
        !            47:        movl    4(fp),r0        /* Fetch "value" */
        !            48:        movl    8(fp),r1        
        !            49: 
        !            50:        andl3   $EXPMASK,r0,r2  /* r2 := shifted biased exponent */
        !            51:        jeql    ld1             /* If it's zero, we're done */
        !            52:        shar    $EXPSHIFT,r2,r2 /* shift to get value of exponent  */
        !            53: 
        !            54:        addl2   12(fp),r2       /* r2 := new biased exponent */
        !            55:        jleq    under           /* if it's <= 0, we have an underflow */
        !            56:        cmpl    r2,$256         /* Otherwise check if it's too big */
        !            57:        jgeq    over            /* jump if overflow */
        !            58: /*
        !            59: *      Construct the result and return
        !            60: */
        !            61:        andl2   $0!EXPMASK,r0   /* clear old exponent */
        !            62:        shal    $EXPSHIFT,r2,r2 /* Put the exponent back in the result */
        !            63:        orl2    r2,r0
        !            64: ld1:   ret
        !            65: /*
        !            66: *      Underflow
        !            67: */
        !            68: under: clrl    r0              /* Result is zero */
        !            69:        clrl    r1
        !            70:        jbr     err             /* Join general error code */
        !            71: /*
        !            72: *      Overflow
        !            73: */
        !            74: over:  movl    huge0,r0        /* Largest possible floating magnitude */
        !            75:        movl    huge1,r1
        !            76:        jbc     $31,4(fp),err   /* Jump if argument was positive */
        !            77:        orl2    $SIGNBIT,r0     /* If arg < 0, make result negative */
        !            78: 
        !            79: err:   movl    $ERANGE,_errno  /* Indicate range error */
        !            80:        ret
        !            81: 
        !            82:        .data
        !            83:        .globl  _errno          /* error flag */
        !            84: huge0: .word   0x7fff          /* The largest number that can */
        !            85:        .word   0xffff          /*   be represented in a long floating */
        !            86: huge1: .word   0xffff          /*   number.  */
        !            87:        .word   0xffff          

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