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/* |
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* Written by J.T. Conklin . |
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* Adapted for use as log2 by Ulrich Drepper . |
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* Public domain. |
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* |
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* Changed to use fyl2xp1 for values near 1, . |
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* |
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* Removed header file dependency for use in libmingwex.a by |
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* Danny Smith |
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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 ħInf */ |
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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 ħInf */ |
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fstp %st(1) |
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fstp %st(1) |
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ret |