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Annotation of 43BSDReno/lib/libc/tahoe/gen/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: (1) source distributions retain this entire copyright
                      7:  * notice and comment, and (2) distributions including binaries display
                      8:  * the following acknowledgement:  ``This product includes software
                      9:  * developed by the University of California, Berkeley and its contributors''
                     10:  * in the documentation or other materials provided with the distribution
                     11:  * and in all advertising materials mentioning features or use of this
                     12:  * software. Neither the name of the University nor the names of its
                     13:  * contributors may be used to endorse or promote products derived
                     14:  * from this software without specific prior written permission.
                     15:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
                     16:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
                     17:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     18:  *
                     19:  * This code is derived from software contributed to Berkeley by
                     20:  * Computer Consoles Inc.
                     21:  */
                     22: 
                     23: #if defined(LIBC_SCCS) && !defined(lint)
                     24:        .asciz "@(#)ldexp.s     5.2 (Berkeley) 6/1/90"
                     25: #endif /* LIBC_SCCS and not lint */
                     26: 
                     27: /*
                     28:  * double ldexp (value, exp)
                     29:  *     double value;
                     30:  *     int exp;
                     31:  *
                     32:  * Ldexp returns value*2**exp, if that result is in range.
                     33:  * If underflow occurs, it returns zero.  If overflow occurs,
                     34:  * it returns a value of appropriate sign and largest
                     35:  * possible magnitude.  In case of either overflow or underflow,
                     36:  * the external int "errno" is set to ERANGE.  Note that errno is
                     37:  * not modified if no error occurs, so if you intend to test it
                     38:  * after you use ldexp, you had better set it to something
                     39:  * other than ERANGE first (zero is a reasonable value to use).
                     40:  *
                     41:  * Constants
                     42:  */
                     43: 
                     44: /*
                     45:  * we can't include errno.h anymore, ANSI says that it defines errno.
                     46:  *
                     47:  * #include <errno.h>
                     48:  */
                     49: #define        ERANGE  34
                     50: #include <tahoemath/fp.h>
                     51: 
                     52: #include "DEFS.h"
                     53: 
                     54: ENTRY(ldexp, 0)
                     55:        movl    4(fp),r0        /* Fetch "value" */
                     56:        movl    8(fp),r1        
                     57: 
                     58:        andl3   $EXPMASK,r0,r2  /* r2 := shifted biased exponent */
                     59:        jeql    ld1             /* If it's zero, we're done */
                     60:        shar    $EXPSHIFT,r2,r2 /* shift to get value of exponent  */
                     61: 
                     62:        addl2   12(fp),r2       /* r2 := new biased exponent */
                     63:        jleq    under           /* if it's <= 0, we have an underflow */
                     64:        cmpl    r2,$256         /* Otherwise check if it's too big */
                     65:        jgeq    over            /* jump if overflow */
                     66: /*
                     67: *      Construct the result and return
                     68: */
                     69:        andl2   $0!EXPMASK,r0   /* clear old exponent */
                     70:        shal    $EXPSHIFT,r2,r2 /* Put the exponent back in the result */
                     71:        orl2    r2,r0
                     72: ld1:   ret
                     73: /*
                     74: *      Underflow
                     75: */
                     76: under: clrl    r0              /* Result is zero */
                     77:        clrl    r1
                     78:        jbr     err             /* Join general error code */
                     79: /*
                     80: *      Overflow
                     81: */
                     82: over:  movl    huge0,r0        /* Largest possible floating magnitude */
                     83:        movl    huge1,r1
                     84:        jbc     $31,4(fp),err   /* Jump if argument was positive */
                     85:        orl2    $SIGNBIT,r0     /* If arg < 0, make result negative */
                     86: 
                     87: err:   movl    $ERANGE,_errno  /* Indicate range error */
                     88:        ret
                     89: 
                     90:        .data
                     91:        .globl  _errno          /* error flag */
                     92: huge0: .word   0x7fff          /* The largest number that can */
                     93:        .word   0xffff          /*   be represented in a long floating */
                     94: huge1: .word   0xffff          /*   number.  */
                     95:        .word   0xffff          

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