.file "nearbyint.s"


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// Contributed 2000 by the Intel Numerics Group, Intel Corporation
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//
// History
//==============================================================
// 10/19/00 Created
// 02/08/01 Corrected behavior for all rounding modes.
// 05/20/02 Cleaned up namespace and sf0 syntax
// 02/10/03 Reordered header: .section, .global, .proc, .align
// 07/25/03 Improved performance
//==============================================================

// API
//==============================================================
// double nearbyint(double x)
//==============================================================

// general input registers:
// r14 - r21

rSignexp   = r14
rExp       = r15
rExpMask   = r16
rBigexp    = r17
rFpsr      = r19
rRcs0      = r20
rRcs0Mask  = r21

// floating-point registers:
// f8 - f10

fXInt      = f9
fNormX     = f10

// predicate registers used:
// p6 - p10

// Overview of operation
//==============================================================
// double nearbyint(double x)
// Return an integer value (represented as a double) that is x
// rounded to integer in current rounding mode
// Inexact is not set, otherwise result identical with rint.
//==============================================================

// double_extended
// if the exponent is > 1003e => 3F(true) = 63(decimal)
// we have a significand of 64 bits 1.63-bits.
// If we multiply by 2^63, we no longer have a fractional part
// So input is an integer value already.

// double
// if the exponent is >= 10033 => 34(true) = 52(decimal)
// 34 + 3ff = 433
// we have a significand of 53 bits 1.52-bits. (implicit 1)
// If we multiply by 2^52, we no longer have a fractional part
// So input is an integer value already.

// single
// if the exponent is > 10016 => 17(true) = 23(decimal)
// we have a significand of 24 bits 1.23-bits. (implicit 1)
// If we multiply by 2^23, we no longer have a fractional part
// So input is an integer value already.

.section .text
GLOBAL_LIBM_ENTRY(nearbyint)

{ .mfi
      getf.exp         rSignexp  = f8        // Get signexp, recompute if unorm
      fclass.m         p7,p0 = f8, 0x0b      // Test x unorm
      addl             rBigexp = 0x10033, r0 // Set exponent at which is integer
}
{ .mfi
      nop.m            0
      fcvt.fx.s1       fXInt  = f8           // Convert to int in significand
      mov              rExpMask    = 0x1FFFF // Form exponent mask
}
;;

{ .mfi
      mov              rFpsr = ar40          // Read fpsr -- check rc.s0
      fclass.m         p6,p0 = f8, 0x1e3     // Test x natval, nan, inf
      nop.i            0
}
{ .mfb
      nop.m            0
      fnorm.s1         fNormX  = f8          // Normalize input
(p7)  br.cond.spnt     RINT_UNORM            // Branch if x unorm
}
;;


RINT_COMMON:
// Return here from RINT_UNORM
{ .mfb
      and              rExp = rSignexp, rExpMask // Get biased exponent
(p6)  fma.d.s0         f8 = f8, f1, f0       // Result if x natval, nan, inf
(p6)  br.ret.spnt      b0                    // Exit if x natval, nan, inf
}
;;

{ .mfi
      mov              rRcs0Mask = 0x0c00     // Mask for rc.s0
      fcvt.xf          f8 = fXInt             // Result assume |x| < 2^52
      cmp.ge           p7,p8 = rExp, rBigexp  // Is |x| >= 2^52?
}
;;

// We must correct result if |x| >= 2^52
{ .mfi
      nop.m            0
(p7)  fma.d.s0         f8 = fNormX, f1, f0    // If |x| >= 2^52, result x
      nop.i            0
}
;;

{ .mfi
      nop.m            0
(p8)  fmerge.s         f8 = fNormX, f8        // Make sign nearbyint(x) = sign x
      nop.i            0
}
;;

{ .mfi
(p8)  and              rRcs0 = rFpsr, rRcs0Mask // Get rounding mode for sf0
      nop.f            0
      nop.i            0
}
;;

// If |x| < 2^52 we must test for other rounding modes
{ .mbb
(p8)  cmp.ne.unc       p10,p0 = rRcs0, r0     // Test for other rounding modes
(p10) br.cond.spnt     RINT_NOT_ROUND_NEAREST // Branch if not round nearest
      br.ret.sptk      b0                     // Exit main path if round nearest
}
;;


RINT_UNORM:
// Here if x unorm
{ .mfb
      getf.exp         rSignexp  = fNormX     // Get signexp, recompute if unorm
      fcmp.eq.s0       p7,p0 = f8, f0         // Dummy op to set denormal flag
      br.cond.sptk     RINT_COMMON            // Return to main path
}
;;

RINT_NOT_ROUND_NEAREST:
// Here if not round to nearest, and |x| < 2^52
// Set rounding mode of s2 to that of s0, and repeat the conversion using s2
{ .mfi
      nop.m            0
      fsetc.s2         0x7f, 0x40
      nop.i            0
}
;;

{ .mfi
      nop.m            0
      fcvt.fx.s2       fXInt  = fNormX        // Convert to int in significand
      nop.i            0
}
;;

{ .mfi
      nop.m            0
      fcvt.xf          f8 = fXInt             // Expected result
      nop.i            0
}
;;

// Be sure sign of result = sign of input.  Fixes cases where result is 0.
{ .mfb
      nop.m            0
      fmerge.s         f8 = fNormX, f8
      br.ret.sptk      b0                     // Exit main path
}
;;

GLOBAL_LIBM_END(nearbyint)