1 files changed, 92 insertions, 0 deletions
diff --git a/test/math/elog.c b/test/math/elog.c
new file mode 100644
index 000000000..8afc1e5b4
--- /dev/null
+++ b/test/math/elog.c
@@ -0,0 +1,92 @@
+/*						xlog.c	*/
+/* natural logarithm */
+/* by Stephen L. Moshier. */
+
+#include "mconf.h"
+#include "ehead.h"
+
+
+
+void elog( x, y )
+unsigned short *x, *y;
+{
+unsigned short xx[NE], z[NE], a[NE], b[NE], t[NE], qj[NE];
+long ex;
+int fex;
+
+
+if( x[NE-1] & (unsigned short )0x8000 )
+	{
+	eclear(y);
+	mtherr( "elog", DOMAIN );
+	return;
+	}
+if( ecmp( x, ezero ) == 0 )
+	{
+	einfin( y );
+	eneg(y);
+	mtherr( "elog", SING );
+	return;
+	}
+if( ecmp( x, eone ) == 0 )
+	{
+	eclear( y );
+	return;
+	}
+
+/* range reduction: log x = log( 2**ex * m ) = ex * log2 + log m */
+efrexp( x, &fex, xx );
+/*
+emov(x, xx );
+ex = xx[NX-1] & 0x7fff;
+ex -= 0x3ffe;
+xx[NX-1] = 0x3ffe;
+*/
+
+/* Adjust range to 1/sqrt(2), sqrt(2) */
+esqrt2[NE-1] -= 1;
+if( ecmp( xx, esqrt2 ) < 0 )
+	{
+	fex -= 1;
+	emul( xx, etwo, xx );
+	}
+esqrt2[NE-1] += 1;
+
+esub( eone, xx, a );
+if( a[NE-1] == 0 )
+	{
+	eclear( y );
+	goto logdon;
+	}
+eadd( eone, xx, b );
+ediv( b, a, y );	/* store (x-1)/(x+1) in y */
+
+emul( y, y, z );
+
+emov( eone, a );
+emov( eone, b );
+emov( eone, qj );
+do
+	{
+	eadd( etwo, qj, qj );	/* 2 * i + 1		*/
+	emul( z, a, a );
+	ediv( qj, a, t );
+	eadd( t, b, b );
+	}
+while( ((b[NE-1] & 0x7fff) - (t[NE-1] & 0x7fff)) < NBITS );
+
+
+emul( b, y, y );
+emul( y, etwo, y );
+
+logdon:
+
+/* now add log of 2**ex */
+if( fex != 0 )
+	{
+	ex = fex;
+	ltoe( &ex, b );
+	emul( elog2, b, b );
+	eadd( b, y, y );
+	}
+}