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Annotation of 43BSDTahoe/lib/libc/gen/gen.tahoe/ldexp.s, revision 1.1.1.1

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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