Merge 216da0b7 (automated)

1 files changed, 70 insertions, 0 deletions

diff --git a/pkg/sentry/time/arith_arm64.go b/pkg/sentry/time/arith_arm64.go
new file mode 100644
index 000000000..b94740c2a
--- /dev/null
+++ b/pkg/sentry/time/arith_arm64.go
@@ -0,0 +1,70 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file provides a generic Go implementation of uint128 divided by uint64.
+
+// The code is derived from Go's generic math/big.divWW_g
+// (src/math/big/arith.go), but is only used on ARM64.
+
+package time
+
+import "math/bits"
+
+type word uint
+
+const (
+	_W  = bits.UintSize // word size in bits
+	_W2 = _W / 2        // half word size in bits
+	_B2 = 1 << _W2      // half digit base
+	_M2 = _B2 - 1       // half digit mask
+)
+
+// nlz returns the number of leading zeros in x.
+// Wraps bits.LeadingZeros call for convenience.
+func nlz(x word) uint {
+	return uint(bits.LeadingZeros(uint(x)))
+}
+
+// q = (u1<<_W + u0 - r)/y
+// Adapted from Warren, Hacker's Delight, p. 152.
+func divWW(u1, u0, v word) (q, r word) {
+	if u1 >= v {
+		return 1<<_W - 1, 1<<_W - 1
+	}
+
+	s := nlz(v)
+	v <<= s
+
+	vn1 := v >> _W2
+	vn0 := v & _M2
+	un32 := u1<<s | u0>>(_W-s)
+	un10 := u0 << s
+	un1 := un10 >> _W2
+	un0 := un10 & _M2
+	q1 := un32 / vn1
+	rhat := un32 - q1*vn1
+
+	for q1 >= _B2 || q1*vn0 > _B2*rhat+un1 {
+		q1--
+		rhat += vn1
+
+		if rhat >= _B2 {
+			break
+		}
+	}
+
+	un21 := un32*_B2 + un1 - q1*v
+	q0 := un21 / vn1
+	rhat = un21 - q0*vn1
+
+	for q0 >= _B2 || q0*vn0 > _B2*rhat+un0 {
+		q0--
+		rhat += vn1
+		if rhat >= _B2 {
+			break
+		}
+	}
+
+	return q1*_B2 + q0, (un21*_B2 + un0 - q0*v) >> s
+}