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64 lines
1.2 KiB
ArmAsm
64 lines
1.2 KiB
ArmAsm
/*
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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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* Adapted for x86-64 by Andreas Jaeger <aj@suse.de>.
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*/
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#include <machine/asm.h>
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#ifdef __ELF__
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.section .rodata
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#else
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.text
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#endif
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.align ALIGNARG(4)
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ASM_TYPE_DIRECTIVE(one,@object)
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one: .double 1.0
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ASM_SIZE_DIRECTIVE(one)
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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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ASM_TYPE_DIRECTIVE(limit,@object)
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limit: .double 0.29
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ASM_SIZE_DIRECTIVE(limit)
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#ifdef PIC
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#define MO(op) op##(%rip)
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#else
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#define MO(op) op
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#endif
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.text
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ENTRY(__ieee754_log2l)
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fldl MO(one)
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fldt 8(%rsp) // 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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andb $1,%ah
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jnz 3f // in case x is NaN or ±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 MO(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 ±Inf
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fstp %st(1)
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fstp %st(1)
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ret
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END (__ieee754_log2l)
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