diff --git a/src/math/gen/Makefile b/src/math/gen/Makefile
index f3c3429..7bae051 100644
--- a/src/math/gen/Makefile
+++ b/src/math/gen/Makefile
@@ -2,7 +2,7 @@ CFLAGS=-I. -Wall -fno-builtin -ffloat-store -D_GNU_SOURCE
 U=mpfr
 T=$(wildcard t*.c)
 
-all: gen check mgen tof toa toe next prev rnd
+all: gen check mgen tof toa toe tox next prev rnd
 
 #tx: tx.c $(U)/lib/libmpfr.a $(U)/lib/libgmp.a
 #	musl-gcc -o $@ $(CFLAGS) -I$(U)/include $^
diff --git a/src/math/gen/tox.c b/src/math/gen/tox.c
new file mode 100644
index 0000000..195f31f
--- /dev/null
+++ b/src/math/gen/tox.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <errno.h>
+
+int main(int argc, char *argv[])
+{
+	int i;
+	union {float f; uint32_t i;} f;
+	union {double f; uint64_t i;} d;
+	union {long double f; struct {uint64_t m; uint16_t se;} i;} ld;
+	char *eptr;
+
+	for (i = 1; i < argc; i++) {
+		errno = 0;
+		f.f = strtof(argv[i], &eptr);
+		printf("0x%08x  (*eptr:%d errno:%d)\n", f.i, *eptr, errno);
+		errno = 0;
+		d.f = strtod(argv[i], &eptr);
+		printf("0x%08x %08x  (*eptr:%d errno:%d)\n",
+			(unsigned)(d.i>>32), (unsigned)d.i, *eptr, errno);
+		errno = 0;
+		ld.f = strtold(argv[i], &eptr);
+		printf("0x%04x %08x %08x  (*eptr:%d errno:%d)\n",
+			ld.i.se, (unsigned)(ld.i.m>>32), (unsigned)ld.i.m, *eptr, errno);
+	}
+	return 0;
+}