.file "logbf.s"
// Copyright (c) 2000 - 2003, Intel Corporation
// All rights reserved.
//
// Contributed 2000 by the Intel Numerics Group, Intel Corporation
//
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// modification, are permitted provided that the following conditions are
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//
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//
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// problem reports or change requests be submitted to it directly at
// http://www.intel.com/software/products/opensource/libraries/num.htm.
//
// History
//==============================================================
// 02/02/00 Initial version
// 02/16/00 Modified to conform to C9X
// 03/16/00 Improved speed
// 04/04/00 Unwind support added
// 05/30/00 Fixed bug when x double-extended denormal
// 08/15/00 Bundle added after call to __libm_error_support to properly
// set [the previously overwritten] GR_Parameter_RESULT.
// 05/20/02 Cleaned up namespace and sf0 syntax
// 01/20/03 Improved performance
//
// API
//==============================================================
// float logbf( float x );
//
// Overview of operation
//==============================================================
// The logbf function extracts the exponent of x as an integer in
// floating-point format.
// logbf computes log2 of x as a float
//
// logbf is similar to ilogbf but differs in the following ways:
// +-inf
// ilogbf: returns INT_MAX
// logbf: returns +inf
// Nan returns FP_LOGBNAN (which is either INT_MAX or INT_MIN)
// ilogbf: returns INT_MAX (7fffffff)
// logbf: returns QNAN (quietized SNAN)
// 0 returns FP_ILOGB0 (which is either INT_MIN or -INT_MAX)
// ilogbf: returns -INT_MAX (80000001)
// logbf: returns -inf, raises the divide-by-zero exception,
// and calls libm_error_support to set domain error
//
// Registers used
//==============================================================
// general registers used:
// r26 -> r38
// r35 -> r38 used as parameters to error path
//
// predicate registers used:
// p6, p7, p8
// floating-point registers used:
// f9, f10, f11
// f8, input
rExpBias = r26
rExpMask = r27
rSignexp_x = r28
rExp_x = r29
rTrueExp_x = r30
rExp_2to64 = r31
GR_SAVE_PFS = r32
GR_SAVE_B0 = r33
GR_SAVE_GP = r34
GR_Parameter_X = r35
GR_Parameter_Y = r36
GR_Parameter_RESULT = r37
GR_Parameter_TAG = r38
fExp_in_signif = f9
fNorm_x = f10
fFloat_Exp = f10
f2to64 = f11
.section .text
GLOBAL_LIBM_ENTRY(logbf)
// X NORMAL
// TrueExp_x = exp(f8) - 0xffff
// sig = TrueExp_x
// f8 = convert_to_fp (sig))
{ .mfi
getf.exp rSignexp_x = f8
fclass.m p8,p0 = f8, 0x0b // Test for x unorm
mov rExpBias = 0xffff // Exponent bias
}
{ .mfi
nop.m 0
fnorm.s1 fNorm_x = f8
mov rExpMask = 0x1ffff // Exponent mask
}
;;
// Form signexp of 2^64 in case need to scale denormal
{ .mfb
mov rExp_2to64 = 0x1003f
fclass.m p6,p0 = f8, 0x1e3 // Test x natval, nan, inf
(p8) br.cond.spnt LOGB_DENORM // Branch if x unorm
}
;;
LOGB_COMMON:
// Return here from LOGB_DENORM
{ .mfi
and rExp_x = rSignexp_x, rExpMask // Get biased exponent
fclass.m p7,p0 = f8, 0x07 // Test x zero
nop.i 0
}
;;
// X NAN or INFINITY, return f8 * f8
{ .mfb
sub rTrueExp_x = rExp_x, rExpBias // Get true exponent
(p6) fma.s.s0 f8= f8,f8,f0 // Result if x natval, nan, inf
(p6) br.ret.spnt b0 // Exit if x natval, nan, inf
}
;;
{ .mib
setf.sig fExp_in_signif = rTrueExp_x // Exponent as integer in fp
nop.i 999
(p7) br.cond.spnt LOGB_ZERO
}
;;
// Result can be represented in less than 24 bits, so no precision completer
// is needed.
{ .mfb
nop.m 0
fcvt.xf f8 = fExp_in_signif
br.ret.sptk b0 // Exit main path, 0 < |x| < inf
}
;;
LOGB_DENORM:
// Form 2^64 in case need to scale denormal
// Check to see if double-extended denormal
{ .mfi
setf.exp f2to64 = rExp_2to64
fclass.m p8,p0 = fNorm_x, 0x0b
nop.i 0
}
;;
{ .mfi
nop.m 0
fcmp.eq.s0 p7,p0 = f8, f0 // Dummy op to set denormal flag
nop.i 0
}
;;
// If double-extended denormal add 64 to exponent bias for scaling
// If double-extended denormal form x * 2^64 which is normal
{ .mfi
(p8) add rExpBias = 64, rExpBias
(p8) fmpy.s1 fNorm_x = fNorm_x, f2to64
nop.i 0
}
;;
// Logic is the same as normal path but use normalized input
{ .mib
getf.exp rSignexp_x = fNorm_x
nop.i 0
br.cond.sptk LOGB_COMMON // Return to main path
}
;;
LOGB_ZERO:
// Here if x zero
// f10 = -|f8|
// f9 = 1.0/f10 = -1.0/|f8| = -inf
{ .mmf
alloc r32=ar.pfs,1,2,4,0
mov GR_Parameter_TAG = 152 // Error code
fmerge.ns f10 = f0,f8
}
;;
{ .mfb
nop.m 0
frcpa.s0 f9,p6 = f1,f10 // Produce -inf, Z flag
br.cond.sptk __libm_error_region // Call error support
}
;;
GLOBAL_LIBM_END(logbf)
libm_alias_float_other (logb, logb)
LOCAL_LIBM_ENTRY(__libm_error_region)
.prologue
{ .mfi
add GR_Parameter_Y=-32,sp // Parameter 2 value
nop.f 0
.save ar.pfs,GR_SAVE_PFS
mov GR_SAVE_PFS=ar.pfs // Save ar.pfs
}
{ .mfi
.fframe 64
add sp=-64,sp // Create new stack
nop.f 0
mov GR_SAVE_GP=gp // Save gp
};;
{ .mmi
stfs [GR_Parameter_Y] = f0,16 // STORE Parameter 2 on stack
add GR_Parameter_X = 16,sp // Parameter 1 address
.save b0, GR_SAVE_B0
mov GR_SAVE_B0=b0 // Save b0
};;
.body
{ .mib
stfs [GR_Parameter_X] = f8 // STORE Parameter 1 on stack
add GR_Parameter_RESULT = 0,GR_Parameter_Y // Parameter 3 address
nop.b 0
}
{ .mib
stfs [GR_Parameter_Y] = f9 // Store Parameter 3 on stack
add GR_Parameter_Y = -16,GR_Parameter_Y
br.call.sptk b0=__libm_error_support# // Call error handling function
};;
{ .mmi
add GR_Parameter_RESULT = 48,sp
nop.m 0
nop.i 0
};;
{ .mmi
ldfs f8 = [GR_Parameter_RESULT] // Get return result off stack
.restore sp
add sp = 64,sp // Restore stack pointer
mov b0 = GR_SAVE_B0 // Restore return address
};;
{ .mib
mov gp = GR_SAVE_GP // Restore gp
mov ar.pfs = GR_SAVE_PFS // Restore ar.pfs
br.ret.sptk b0
};;
LOCAL_LIBM_END(__libm_error_region)
.type __libm_error_support#,@function
.global __libm_error_support#