52 lines
1.1 KiB
ArmAsm
52 lines
1.1 KiB
ArmAsm
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/*
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* Written by J.T. Conklin <jtc@netbsd.org>.
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* Adapted for use as log2 by Ulrich Drepper <drepper@cygnus.com>.
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* Public domain.
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*
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* Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>.
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*
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* Removed header file dependency for use in libmingwex.a by
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* Danny Smith <dannysmith@users.sourceforge.net>
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*/
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.file "log2.S"
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.text
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.align 4
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one: .double 1.0
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/* It is not important that this constant is precise. It is only
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a value which is known to be on the safe side for using the
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fyl2xp1 instruction. */
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limit: .double 0.29
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.text
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.align 4
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.globl _log2
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.def _log2; .scl 2; .type 32; .endef
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_log2:
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fldl one
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fldl 4(%esp) // x : 1
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fxam
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fnstsw
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fld %st // x : x : 1
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sahf
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jc 3f // in case x is NaN or <EFBFBD>Inf
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4: fsub %st(2), %st // x-1 : x : 1
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fld %st // x-1 : x-1 : x : 1
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fabs // |x-1| : x-1 : x : 1
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fcompl limit // x-1 : x : 1
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fnstsw // x-1 : x : 1
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andb $0x45, %ah
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jz 2f
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fstp %st(1) // x-1 : 1
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fyl2xp1 // log(x)
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ret
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2: fstp %st(0) // x : 1
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fyl2x // log(x)
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ret
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3: jp 4b // in case x is <EFBFBD>Inf
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fstp %st(1)
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fstp %st(1)
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ret
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