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PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 44 insertions, 0 deletions

diff --git a/pkg/sentry/time/muldiv_amd64.s b/pkg/sentry/time/muldiv_amd64.s
new file mode 100644
index 000000000..291940b1d
--- /dev/null
+++ b/pkg/sentry/time/muldiv_amd64.s
@@ -0,0 +1,44 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "textflag.h"
+
+// Documentation is available in parameters.go.
+//
+// func muldiv64(value, multiplier, divisor uint64) (uint64, bool)
+TEXT ·muldiv64(SB),NOSPLIT,$0-33
+	MOVQ value+0(FP), AX
+	MOVQ multiplier+8(FP), BX
+	MOVQ divisor+16(FP), CX
+
+	// Multiply AX*BX and store result in DX:AX.
+	MULQ BX
+
+	// If divisor <= (value*multiplier) / 2^64, then the division will overflow.
+	//
+	// (value*multiplier) / 2^64 is DX:AX >> 64, or simply DX.
+	CMPQ CX, DX
+	JLE overflow
+
+	// Divide DX:AX by CX.
+	DIVQ CX
+
+	MOVQ AX, result+24(FP)
+	MOVB $1, ok+32(FP)
+	RET
+
+overflow:
+	MOVQ $0, result+24(FP)
+	MOVB $0, ok+32(FP)
+	RET