| 1 | /* |
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| 2 | * Public domain. |
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| 3 | */ |
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| 4 | |
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| 5 | #include <machine/asm.h> |
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| 6 | #include <libm-alias-finite.h> |
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| 7 | |
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| 8 | .section .rodata.cst8,"aM" ,@progbits,8 |
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| 9 | |
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| 10 | .p2align 3 |
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| 11 | .type one,@object |
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| 12 | one: .double 1.0 |
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| 13 | ASM_SIZE_DIRECTIVE(one) |
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| 14 | /* It is not important that this constant is precise. It is only |
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| 15 | a value which is known to be on the safe side for using the |
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| 16 | fyl2xp1 instruction. */ |
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| 17 | .type limit,@object |
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| 18 | limit: .double 0.29 |
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| 19 | ASM_SIZE_DIRECTIVE(limit) |
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| 20 | |
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| 21 | |
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| 22 | #ifdef PIC |
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| 23 | # define MO(op) op##@GOTOFF(%edx) |
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| 24 | #else |
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| 25 | # define MO(op) op |
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| 26 | #endif |
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| 27 | |
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| 28 | .text |
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| 29 | ENTRY(__ieee754_log2) |
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| 30 | #ifdef PIC |
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| 31 | LOAD_PIC_REG (dx) |
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| 32 | #endif |
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| 33 | fldl MO(one) |
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| 34 | fldl 4(%esp) // x : 1 |
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| 35 | fxam |
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| 36 | fnstsw |
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| 37 | fld %st // x : x : 1 |
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| 38 | sahf |
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| 39 | jc 3f // in case x is NaN or ħInf |
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| 40 | 4: fsub %st(2), %st // x-1 : x : 1 |
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| 41 | fld %st // x-1 : x-1 : x : 1 |
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| 42 | fabs // |x-1| : x-1 : x : 1 |
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| 43 | fcompl MO(limit) // x-1 : x : 1 |
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| 44 | fnstsw // x-1 : x : 1 |
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| 45 | andb $0x45, %ah |
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| 46 | jz 2f |
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| 47 | fxam |
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| 48 | fnstsw |
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| 49 | andb $0x45, %ah |
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| 50 | cmpb $0x40, %ah |
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| 51 | jne 5f |
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| 52 | fabs // log2(1) is +0 in all rounding modes. |
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| 53 | 5: fstp %st(1) // x-1 : 1 |
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| 54 | fyl2xp1 // log(x) |
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| 55 | ret |
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| 56 | |
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| 57 | 2: fstp %st(0) // x : 1 |
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| 58 | fyl2x // log(x) |
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| 59 | ret |
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| 60 | |
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| 61 | 3: jp 4b // in case x is ħInf |
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| 62 | fstp %st(1) |
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| 63 | fstp %st(1) |
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| 64 | ret |
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| 65 | END (__ieee754_log2) |
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| 66 | libm_alias_finite (__ieee754_log2, __log2) |
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| 67 | |
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