usr/src/sys/tahoe/math/Kldexpf.s

/*      Kldexpf.s       1.4     90/12/04        */

#include "../tahoe/SYS.h"
#include "../math/fp.h"
#include "../math/Kfp.h"

/* @(*)Kldexpf.s        4.2 (Berkeley) 12/21/80
 *      Tahoe           2/2/83
 *
 * float Kldexpf (op_most, op_least, exp, hfs)
 *
 * Ldexp returns value*2**exp, if that result is in range.
 * If underflow occurs, it returns zero.  If overflow occurs,
 * it returns a value of appropriate sign and largest
 * possible magnitude.  In case of either overflow or underflow,
 * the external int "errno" is set to ERANGE.  Note that errno is
 * not modified if no error occurs, so if you intend to test it
 * after you use Kldexpf, you had better set it to something
 * other than ERANGE first (zero is a reasonable value to use).
 */

        .text
ENTRY(Kldexpf, R2)
        movl    4(fp),r0        /* Fetch "value" */
        movl    8(fp),r1

        andl3   $EXPMASK,r0,r2  /* r2 := shifted biased exponent */
        jeql    ld1             /* If it's zero, we're done */
        shar    $EXPSHIFT,r2,r2 /* shift to get value of exponent  */

        addl2   12(fp),r2       /* r2 := new biased exponent */
        jleq    under           /* if it's <= 0, we have an underflow */
        cmpl    r2,$256         /* Otherwise check if it's too big */
        jgeq    over            /* jump if overflow */
/*
 *      Construct the result and return
 */
        andl2   $0!EXPMASK,r0   /* clear old exponent */
        shal    $EXPSHIFT,r2,r2 /* Put the exponent back in the result */
        orl2    r2,r0
ld1:    ret
/*
 *      Underflow
 */
under:  clrl    r0              /* Result is zero */
        clrl    r1
        orl2    $HFS_UNDF,*16(fp)
        jmp     err             /* Join general error code */
/*
 *      Overflow
 */
over:   movl    huge0,r0        /* Largest possible floating magnitude */
        movl    huge1,r1
        orl2    $HFS_OVF,*16(fp)
        orl2    $SIGNBIT,r0     /* If arg < 0, make result negative */

err:    orl2    $HFS_RANGE,*16(fp)      /* Indicate range error */
        ret

        .data
huge0:  .long   0x7fffffff
huge1:  .long   0xffffffff