Call isatty() way less frequently

1 files changed, 2 insertions, 1 deletions

diff --git a/main.c b/main.c
index 9608211..3e33516 100644
--- a/main.c
+++ b/main.c
@@ -139,6 +139,7 @@ error_io:
 static ssize_t dump_fd(int fd) {
     void *buf;
     ssize_t total  = 0;
+    int tty = isatty(fileno(stdout));
     struct stat st;
 
     if (fstat(fd, &st) < 0) {
@@ -163,7 +164,7 @@ static ssize_t dump_fd(int fd) {
             size_t left   = len - i,
                    linesz = left < ZXDUMP_STRIDE_LINE?  left: ZXDUMP_STRIDE_LINE;
 
-            if (dump_line(offset, buf, linesz, isatty(fileno(stdout))) < 0) {
+            if (dump_line(offset, buf, linesz, tty) < 0) {
                 goto error_dump_line;
             }