libc: fix spim endianness

1 files changed, 103 insertions, 0 deletions

diff --git a/sys/src/libc/spim/sqrt.c b/sys/src/libc/spim/sqrt.c
new file mode 100644
index 000000000..6f6fc6be6
--- /dev/null
+++ b/sys/src/libc/spim/sqrt.c
@@ -0,0 +1,103 @@
+#include <u.h>
+#include <libc.h>
+
+static	long	sqtab[64] =
+{
+	0x6cdb2, 0x726d4, 0x77ea3, 0x7d52f, 0x82a85, 0x87eb1, 0x8d1c0, 0x923bd,
+	0x974b2, 0x9c4a8, 0xa13a9, 0xa61be, 0xaaeee, 0xafb41, 0xb46bf, 0xb916e,
+	0xbdb55, 0xc247a, 0xc6ce3, 0xcb495, 0xcfb95, 0xd41ea, 0xd8796, 0xdcca0,
+	0xe110c, 0xe54dd, 0xe9818, 0xedac0, 0xf1cd9, 0xf5e67, 0xf9f6e, 0xfdfef,
+	0x01fe0, 0x05ee6, 0x09cfd, 0x0da30, 0x11687, 0x1520c, 0x18cc8, 0x1c6c1,
+	0x20000, 0x2388a, 0x27068, 0x2a79e, 0x2de32, 0x3142b, 0x3498c, 0x37e5b,
+	0x3b29d, 0x3e655, 0x41989, 0x44c3b, 0x47e70, 0x4b02b, 0x4e16f, 0x51241,
+	0x542a2, 0x57296, 0x5a220, 0x5d142, 0x60000, 0x62e5a, 0x65c55, 0x689f2,
+};
+
+double
+sqrt(double arg)
+{
+	int e, ms;
+	double a, t;
+	union
+	{
+		double	d;
+		struct
+		{
+			long	ls;
+			long	ms;
+		};
+	} u;
+
+	u.d = arg;
+	ms = u.ms;
+
+	/*
+	 * sign extend the mantissa with
+	 * exponent. result should be > 0 for
+	 * normal case.
+	 */
+	e = ms >> 20;
+	if(e <= 0) {
+		if(e == 0)
+			return 0;
+		return NaN();
+	}
+
+	/*
+	 * pick up arg/4 by adjusting exponent
+	 */
+	u.ms = ms - (2 << 20);
+	a = u.d;
+
+	/*
+	 * use 5 bits of mantissa and 1 bit
+	 * of exponent to form table index.
+	 * insert exponent/2 - 1.
+	 */
+	e = (((e - 1023) >> 1) + 1022) << 20;
+	u.ms = *(long*)((char*)sqtab + ((ms >> 13) & 0xfc)) | e;
+	u.ls = 0;
+
+	/*
+	 * three laps of newton
+	 */
+	e = 1 << 20;
+	t = u.d;
+	u.d = t + a/t;
+	u.ms -= e;		/* u.d /= 2; */
+	t = u.d;
+	u.d = t + a/t;
+	u.ms -= e;		/* u.d /= 2; */
+	t = u.d;
+
+	return t + a/t;
+}
+
+/*
+ * this is the program that generated the table.
+ * it calls sqrt by some other means.
+ * 
+ * void
+ * main(void)
+ * {
+ * 	int i;
+ * 	union	U
+ * 	{
+ * 		double	d;
+ * 		struct
+ * 		{
+ * 			long	ms;
+ * 			long	ls;
+ * 		};
+ * 	} u;
+ * 
+ * 	for(i=0; i<64; i++) {
+ * 		u.ms = (i<<15) | 0x3fe04000;
+ * 		u.ls = 0;
+ * 		u.d = sqrt(u.d);
+ * 		print(" 0x%.5lux,", u.ms & 0xfffff);
+ * 	}
+ * 	print("\n");
+ * 	exits(0);
+ * }
+ */