From 96ccc85d6a58b7ebfcb69d6d470ff209668f6187 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Thu, 23 Nov 2023 11:43:50 +0000
Subject: initial SIMD trials of some libgeometry functions.

---
 nanosec.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 nanosec.c

(limited to 'nanosec.c')

diff --git a/nanosec.c b/nanosec.c
new file mode 100644
index 0000000..f82d47a
--- /dev/null
+++ b/nanosec.c
@@ -0,0 +1,109 @@
+#include <u.h>
+#include <libc.h>
+#include <tos.h>
+
+/*
+ * This code is a mixture of cpuid(1) and the nanosec() found in vmx,
+ * in order to force the use of nsec(2) in case we are running in a
+ * virtualized environment where the clock is mis-bhyve-ing.
+ */
+
+typedef struct Res {
+	ulong ax, bx, cx, dx;
+} Res;
+
+static uchar _cpuid[] = {
+	0x5E,			/* POP SI (PC) */
+	0x5D,			/* POP BP (Res&) */
+	0x58,			/* POP AX */
+	0x59,			/* POP CX */
+
+	0x51,			/* PUSH CX */
+	0x50,			/* PUSH AX */
+	0x55,			/* PUSH BP */
+	0x56,			/* PUSH SI */
+
+	0x31, 0xDB,		/* XOR BX, BX */
+	0x31, 0xD2,		/* XOR DX, DX */
+
+	0x0F, 0xA2,		/* CPUID */
+
+	0x89, 0x45, 0x00,	/* MOV AX, 0(BP) */
+	0x89, 0x5d, 0x04,	/* MOV BX, 4(BP) */
+	0x89, 0x4d, 0x08,	/* MOV CX, 8(BP) */
+	0x89, 0x55, 0x0C,	/* MOV DX, 12(BP) */
+	0xC3,			/* RET */
+};
+
+static Res (*cpuid)(ulong ax, ulong cx) = (Res(*)(ulong, ulong)) _cpuid;
+
+/*
+ * nsec() is wallclock and can be adjusted by timesync
+ * so need to use cycles() instead, but fall back to
+ * nsec() in case we can't
+ */
+uvlong
+nanosec(void)
+{
+	static uvlong fasthz, xstart;
+	char buf[13], path[128];
+	ulong w;
+	uvlong x, div;
+	int fd;
+	Res r;
+
+	if(fasthz == ~0ULL)
+		return nsec() - xstart;
+
+	if(fasthz == 0){
+		/* first long in a.out header */
+		snprint(path, sizeof path, "/proc/%d/text", getpid());
+		fd = open(path, OREAD);
+		if(fd < 0)
+			goto Wallclock;
+		if(read(fd, buf, 4) != 4){
+			close(fd);
+			goto Wallclock;
+		}
+		close(fd);
+
+		w = ((ulong *) buf)[0];
+
+		switch(w){
+		default:
+			goto Wallclock;
+		case 0x978a0000:	/* amd64 */
+			/* patch out POP BP -> POP AX */
+			_cpuid[1] = 0x58;
+		case 0xeb010000:	/* 386 */
+			break;
+		}
+		segflush(_cpuid, sizeof(_cpuid));
+
+		r = cpuid(0x40000000, 0);
+		((ulong *) buf)[0] = r.bx;
+		((ulong *) buf)[1] = r.cx;
+		((ulong *) buf)[2] = r.dx;
+		buf[12] = 0;
+
+		if(strstr(buf, "bhyve") != nil)
+			goto Wallclock;
+
+		if(_tos->cyclefreq){
+			fasthz = _tos->cyclefreq;
+			cycles(&xstart);
+		} else {
+Wallclock:
+			fasthz = ~0ULL;
+			xstart = nsec();
+		}
+		return 0;
+	}
+	cycles(&x);
+	x -= xstart;
+
+	/* this is ugly */
+	for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
+
+	return x / (fasthz / div);
+}
-- 
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