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math: handle denormals in AMD64 Exp
Fixes #23164 Change-Id: I6e8c6443f3ef91df71e117cce1cfa1faba647dd7 Reviewed-on: https://go-review.googlesource.com/87337 Reviewed-by: Robert Griesemer <gri@golang.org> Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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@ -1014,6 +1014,8 @@ var vfexpSC = []float64{
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1,
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// near zero
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3.725290298461915e-09,
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// denormal
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-740,
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}
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var expSC = []float64{
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0,
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@ -1026,6 +1028,7 @@ var expSC = []float64{
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Inf(1),
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2.718281828459045,
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1.0000000037252903,
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4.2e-322,
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}
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var vfexp2SC = []float64{
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@ -96,14 +96,13 @@ TEXT ·Exp(SB),NOSPLIT,$0
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MULSD X1, X0
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ADDSD exprodata<>+8(SB), X0
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// return fr * 2**exponent
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lastStep:
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MOVL $0x3FF, AX // bias
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ADDL AX, BX
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JLE underflow
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ldexp:
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ADDL $0x3FF, BX // add bias
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JLE denormal
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CMPL BX, $0x7FF
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JGE overflow
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MOVL $52, CX
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SHLQ CX, BX
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lastStep:
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SHLQ $52, BX
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MOVQ BX, X1
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MULSD X1, X0
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MOVSD X0, ret+8(FP)
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@ -115,14 +114,22 @@ notFinite:
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JNE notNegInf
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// -Inf, return 0
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underflow: // return 0
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MOVQ $0, AX
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MOVQ AX, ret+8(FP)
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MOVQ $0, ret+8(FP)
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RET
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overflow: // return +Inf
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MOVQ $PosInf, BX
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notNegInf: // NaN or +Inf, return x
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MOVQ BX, ret+8(FP)
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RET
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denormal:
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CMPL BX, $-52
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JL underflow
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ADDL $0x3FE, BX // add bias - 1
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SHLQ $52, BX
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MOVQ BX, X1
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MULSD X1, X0
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MOVQ $1, BX
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JMP lastStep
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avxfma:
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MOVSD $LN2U, X2
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@ -149,4 +156,4 @@ avxfma:
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MULSD X1, X0
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VADDSD exprodata<>+16(SB), X0, X1
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VFMADD213SD exprodata<>+8(SB), X1, X0
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JMP lastStep
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JMP ldexp
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