.file "libm_frexp.s"

// Copyright (c) 2000 - 2003, Intel Corporation

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//

// Contributed 2000 by the Intel Numerics Group, Intel Corporation

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//

// History

//==============================================================

// 02/02/00 Initial version

// 03/20/00 Improved speed

// 06/01/00 Fixed bug when x a double-extended denormal

// 12/08/00 Corrected label on .endp

// 01/23/02 Added handling for int 32 or 64 bits

// 05/20/02 Cleaned up namespace and sf0 syntax

// 02/10/03 Reordered header: .section, .global, .proc, .align

//

// API

//==============================================================

// double __libm_frexp(double x, int* y, int int_type)

// input  floating point f8, pointer to y (r33), int int_type (r34)

// output floating point f8, returns the fraction of x, 0.5 <= fraction < 1.0

// output int* y, returns the true exponent of x

//

// int_type = 0 if int is 32 bits

// int_type = 1 if int is 64 bits

//

// int* y is returned as a 32 bit integer if int_type = 0

// int* y is returned as a 64 bit integer if int_type = 1

//

// Overview of operation

//==============================================================

// break a floating point x number into fraction and an exponent

// The fraction is returned as a double

// The exponent is returned as an integer pointed to by y

//    This is a true (not a biased exponent) but 0fffe is subtracted

//    as a bias instead of 0xffff. This is because the fraction returned

//    is between 0.5 and 1.0, not the expected IEEE range.

//

// The fraction is 0.5 <= fraction < 1.0

//

// Registers used

//==============================================================

//

// general registers:

// r14  exponent bias for x negative

// r15  exponent bias for x positive

// r16  signexp of x

// r17  exponent mask

// r18  exponent of x

// r19  exponent result

// r20  signexp of 2^64

// r32  on input contains the 64-bit IEEE double that is in f8

// r33  on input pointer to 32-bit or 64-bit integer for exponent

// r34  on input contains 0 if output int is 32 bits, else output int is 64 bits

//

// predicate registers:

// p6   set if x is Nan, zero, or infinity

// p7   set if x negative

// p8   set if x positive

// p9   set if x double-extended denormal

// p10  set if int_type = 0, 32-bit integer

// p11  set if int_type = 1, 64-bit integer

//

// floating-point registers:

// f8  input, output

// f9  normalized x

// f10 signexp for significand result for x positive

// f11 signexp for significand result for x negative

// f12 2^64

.section .text

GLOBAL_LIBM_ENTRY(__libm_frexp)

// Set signexp for significand result for x>0

// If x is a NaN, zero, or infinity, return it.

// Put 0 in the int pointer.

// x NAN, ZERO, INFINITY?

// Set signexp for significand result for x<0

{ .mfi

        mov         r15 = 0x0fffe

        fclass.m    p6,p7 = f8, 0xe7

        mov         r14 = 0x2fffe

}

// Form signexp of 2^64 in case x double-extended denormal

// Save the normalized value of input in f9

// The normalization also sets fault flags and takes faults if necessary

{ .mfi

        mov         r20 = 0x1003f

        fnorm.s0    f9 = f8

        nop.i 999 ;;

}

// Move signexp for significand result for x>0 to FP reg

// Form 2^64 in case x double-extended denormal

{ .mmi

        setf.exp    f10 = r15

        setf.exp    f12 = r20

        nop.i 999 ;;

}

// Move signexp for significand result for x<0 to FP reg

// p7 if x<0, else p8

// If x=0,nan,inf, set p10 if output int to be 32 bits, or set p11 if 64 bits

{ .mfi

        setf.exp    f11 = r14

(p7)    fcmp.lt.s0  p7,p8 = f8,f0

(p6)    cmp.eq.unc  p10,p11 = r34, r0 ;;

}

// If x NAN, ZERO, INFINITY, set *y=0 and exit

{ .mmb

(p10)   st4         [r33] = r0      // Store *y=0 as 32-bit integer

(p11)   st8         [r33] = r0      // Store *y=0 as 64-bit integer

(p6)    br.ret.spnt b0 ;;

}

// Form exponent mask

// Test for fnorm(x) denormal, means x double-extended denormal

{ .mfi

        mov         r17 = 0x1ffff

        fclass.m    p9,p0 = f9, 0x0b

        nop.i 999 ;;

}

// If x double-extended denormal add 64 to exponent bias for scaling

// If x double-extended denormal multiply x * 2^64 which is normal

// Set p10 if output int to be 32 bits, or set p11 if 64 bits

{ .mfi

(p9)    add         r15 = 64, r15

(p9)    fmpy.s0     f9 = f9, f12

        cmp.eq      p10,p11 = r34, r0 ;;

}

// true exponent stored to int pointer

// the bias is treated as 0xfffe instead of

// normal 0xffff because we want the significand

// to be in the range <=0.5 sig < 1.0

// Store the value of the exponent at the pointer in r33

// If x>0 form significand result

{ .mfi

        nop.m 999

(p8)    fmerge.se   f8 = f10,f9

        nop.i 999  ;;

}

// Get signexp of normalized x

// If x<0 form significand result

{ .mfi

        getf.exp    r16 = f9

(p7)    fmerge.se   f8 = f11,f9

        nop.i 999  ;;

}

// Get exp of normalized x

// Subtract off bias to get true exponent of x

{ .mmi

        and         r18 = r17,r16 ;;

        sub         r19 = r18,r15

        nop.i 999  ;;

}

// Store int *y as a 32-bit integer

// Make the value a double

{ .mfi

(p10)   st4         [r33] = r19        // Store *y as 32-bit integer

        fnorm.d.s0  f8 = f8

        nop.i 999

}

{ .mfb

(p11)   st8         [r33] = r19        // Store *y as 64-bit integer

        nop.f 999

        br.ret.sptk b0 ;;

}

GLOBAL_LIBM_END(__libm_frexp)