Add a "fork" of musl as //fusl.

fusl/src/math/x86_64/expl.s

Index: fusl/src/math/x86_64/expl.s
diff --git a/fusl/src/math/x86_64/expl.s b/fusl/src/math/x86_64/expl.s
new file mode 100644
index 0000000000000000000000000000000000000000..798261d2835346a9d219f1e45b276c09b6b795c2
--- /dev/null
+++ b/fusl/src/math/x86_64/expl.s
@@ -0,0 +1,101 @@
+# exp(x) = 2^hi + 2^hi (2^lo - 1)
+# where hi+lo = log2e*x with 128bit precision
+# exact log2e*x calculation depends on nearest rounding mode
+# using the exact multiplication method of Dekker and Veltkamp
+
+.global expl
+.type expl,@function
+expl:
+	fldt 8(%rsp)
+
+		# interesting case: 0x1p-32 <= |x| < 16384
+		# check if (exponent|0x8000) is in [0xbfff-32, 0xbfff+13]
+	mov 16(%rsp), %ax
+	or $0x8000, %ax
+	sub $0xbfdf, %ax
+	cmp $45, %ax
+	jbe 2f
+	test %ax, %ax
+	fld1
+	js 1f
+		# if |x|>=0x1p14 or nan return 2^trunc(x)
+	fscale
+	fstp %st(1)
+	ret
+		# if |x|<0x1p-32 return 1+x
+1:	faddp
+	ret
+
+		# should be 0x1.71547652b82fe178p0L == 0x3fff b8aa3b29 5c17f0bc
+		# it will be wrong on non-nearest rounding mode
+2:	fldl2e
+	subq $48, %rsp
+		# hi = log2e_hi*x
+		# 2^hi = exp2l(hi)
+	fmul %st(1),%st
+	fld %st(0)
+	fstpt (%rsp)
+	fstpt 16(%rsp)
+	fstpt 32(%rsp)
+	call exp2l@PLT
+		# if 2^hi == inf return 2^hi
+	fld %st(0)
+	fstpt (%rsp)
+	cmpw $0x7fff, 8(%rsp)
+	je 1f
+	fldt 32(%rsp)
+	fldt 16(%rsp)
+		# fpu stack: 2^hi x hi
+		# exact mult: x*log2e
+	fld %st(1)
+		# c = 0x1p32+1
+	movq $0x41f0000000100000,%rax
+	pushq %rax
+	fldl (%rsp)
+		# xh = x - c*x + c*x
+		# xl = x - xh
+	fmulp
+	fld %st(2)
+	fsub %st(1), %st
+	faddp
+	fld %st(2)
+	fsub %st(1), %st
+		# yh = log2e_hi - c*log2e_hi + c*log2e_hi
+	movq $0x3ff7154765200000,%rax
+	pushq %rax
+	fldl (%rsp)
+		# fpu stack: 2^hi x hi xh xl yh
+		# lo = hi - xh*yh + xl*yh
+	fld %st(2)
+	fmul %st(1), %st
+	fsubp %st, %st(4)
+	fmul %st(1), %st
+	faddp %st, %st(3)
+		# yl = log2e_hi - yh
+	movq $0x3de705fc2f000000,%rax
+	pushq %rax
+	fldl (%rsp)
+		# fpu stack: 2^hi x lo xh xl yl
+		# lo += xh*yl + xl*yl
+	fmul %st, %st(2)
+	fmulp %st, %st(1)
+	fxch %st(2)
+	faddp
+	faddp
+		# log2e_lo
+	movq $0xbfbe,%rax
+	pushq %rax
+	movq $0x82f0025f2dc582ee,%rax
+	pushq %rax
+	fldt (%rsp)
+	addq $40,%rsp
+		# fpu stack: 2^hi x lo log2e_lo
+		# lo += log2e_lo*x
+		# return 2^hi + 2^hi (2^lo - 1)
+	fmulp %st, %st(2)
+	faddp
+	f2xm1
+	fmul %st(1), %st
+	faddp
+1:	addq $48, %rsp
+	ret