Avoid compilation warnings in SCM_MAKE_CHAR

* libguile/chars.h (SCM_MAKE_CHAR): change inequality

1 files changed, 9 insertions, 3 deletions

diff --git a/libguile/chars.h b/libguile/chars.h
index 51adc21e5..f75aeadd1 100644
--- a/libguile/chars.h
+++ b/libguile/chars.h
@@ -32,9 +32,15 @@
 #define SCM_CHARP(x) (SCM_ITAG8(x) == scm_tc8_char)
 #define SCM_CHAR(x) ((scm_t_wchar)SCM_ITAG8_DATA(x))
 
-#define SCM_MAKE_CHAR(x)                                               \
-  ((scm_t_int32) (x) < 0                                               \
-   ? SCM_MAKE_ITAG8 ((scm_t_bits) (unsigned char) (x), scm_tc8_char)   \
+/* SCM_MAKE_CHAR maps signed chars (-128 to 127) and unsigned chars (0
+   to 255) to Latin-1 codepoints (0 to 255) while allowing higher
+   codepoints (256 to 1114111) to pass through unchanged.
+
+   This macro evaluates x twice, which may lead to side effects if not
+   used properly. */
+#define SCM_MAKE_CHAR(x)                                                \
+  ((x) <= 1                                                             \
+   ? SCM_MAKE_ITAG8 ((scm_t_bits) (unsigned char) (x), scm_tc8_char)    \
    : SCM_MAKE_ITAG8 ((scm_t_bits) (x), scm_tc8_char))
 
 #define SCM_CODEPOINT_MAX (0x10ffff)