util: move brw_env_var_as_boolean() to util

Kind of a handy function.  And I'll want it available outside of i965
for common nir-pass helpers.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Nicolai Hähnle <nhaehnle@gmail.com>

src/util/debug.c

@@ -51,3 +51,28 @@ parse_debug_string(const char *debug,
 
    return flag;
 }
+
+/**
+ * Reads an environment variable and interprets its value as a boolean.
+ *
+ * Recognizes 0/false/no and 1/true/yes.  Other values result in the default value.
+ */
+bool
+env_var_as_boolean(const char *var_name, bool default_value)
+{
+   const char *str = getenv(var_name);
+   if (str == NULL)
+      return default_value;
+
+   if (strcmp(str, "1") == 0 ||
+       strcasecmp(str, "true") == 0 ||
+       strcasecmp(str, "yes") == 0) {
+      return true;
+   } else if (strcmp(str, "0") == 0 ||
+              strcasecmp(str, "false") == 0 ||
+              strcasecmp(str, "no") == 0) {
+      return false;
+   } else {
+      return default_value;
+   }
+}

src/util/debug.h

@@ -38,6 +38,8 @@ struct debug_control {
 uint64_t
 parse_debug_string(const char *debug,
                    const struct debug_control *control);
+bool
+env_var_as_boolean(const char *var_name, bool default_value);
 
 #ifdef __cplusplus
 } /* extern C */