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93 lines
2.7 KiB
ArmAsm
93 lines
2.7 KiB
ArmAsm
/*
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* Written by J.T. Conklin <jtc@netbsd.org>.
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* Public domain.
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*
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* Adapted for `long double' by Ulrich Drepper <drepper@cygnus.com>.
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*/
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/*
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* The 8087 method for the exponential function is to calculate
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* exp(x) = 2^(x log2(e))
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* after separating integer and fractional parts
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* x log2(e) = i + f, |f| <= .5
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* 2^i is immediate but f needs to be precise for long double accuracy.
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* Suppress range reduction error in computing f by the following.
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* Separate x into integer and fractional parts
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* x = xi + xf, |xf| <= .5
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* Separate log2(e) into the sum of an exact number c0 and small part c1.
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* c0 + c1 = log2(e) to extra precision
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* Then
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* f = (c0 xi - i) + c0 xf + c1 x
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* where c0 xi is exact and so also is (c0 xi - i).
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* -- moshier@na-net.ornl.gov
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*/
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#include <machine/asm.h>
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.section .rodata.cst16,"aM",@progbits,16
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.p2align 4
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ASM_TYPE_DIRECTIVE(c0,@object)
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c0: .byte 0, 0, 0, 0, 0, 0, 0xaa, 0xb8, 0xff, 0x3f
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.byte 0, 0, 0, 0, 0, 0
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ASM_SIZE_DIRECTIVE(c0)
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ASM_TYPE_DIRECTIVE(c1,@object)
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c1: .byte 0x20, 0xfa, 0xee, 0xc2, 0x5f, 0x70, 0xa5, 0xec, 0xed, 0x3f
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.byte 0, 0, 0, 0, 0, 0
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ASM_SIZE_DIRECTIVE(c1)
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#ifdef PIC
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# define MO(op) op##@GOTOFF(%ecx)
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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_expl)
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fldt 4(%esp)
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/* I added the following ugly construct because expl(+-Inf) resulted
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in NaN. The ugliness results from the bright minds at Intel.
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For the i686 the code can be written better.
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-- drepper@cygnus.com. */
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fxam /* Is NaN or +-Inf? */
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#ifdef PIC
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LOAD_PIC_REG (cx)
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#endif
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fstsw %ax
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movb $0x45, %dh
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andb %ah, %dh
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cmpb $0x05, %dh
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je 1f /* Is +-Inf, jump. */
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fldl2e /* 1 log2(e) */
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fmul %st(1), %st /* 1 x log2(e) */
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frndint /* 1 i */
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fld %st(1) /* 2 x */
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frndint /* 2 xi */
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fld %st(1) /* 3 i */
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fldt MO(c0) /* 4 c0 */
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fld %st(2) /* 5 xi */
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fmul %st(1), %st /* 5 c0 xi */
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fsubp %st, %st(2) /* 4 f = c0 xi - i */
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fld %st(4) /* 5 x */
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fsub %st(3), %st /* 5 xf = x - xi */
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fmulp %st, %st(1) /* 4 c0 xf */
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faddp %st, %st(1) /* 3 f = f + c0 xf */
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fldt MO(c1) /* 4 */
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fmul %st(4), %st /* 4 c1 * x */
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faddp %st, %st(1) /* 3 f = f + c1 * x */
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f2xm1 /* 3 2^(fract(x * log2(e))) - 1 */
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fld1 /* 4 1.0 */
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faddp /* 3 2^(fract(x * log2(e))) */
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fstp %st(1) /* 2 */
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fscale /* 2 scale factor is st(1); e^x */
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fstp %st(1) /* 1 */
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fstp %st(1) /* 0 */
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jmp 2f
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1: testl $0x200, %eax /* Test sign. */
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jz 2f /* If positive, jump. */
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fstp %st
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fldz /* Set result to 0. */
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2: ret
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END(__ieee754_expl)
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strong_alias (__ieee754_expl, __expl_finite)
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