gen_qfloat16_tables: add a comment explaining what the tool is

For our future selves.

Change-Id: I2b1955a995ad40f3b89afffd15a4c127686662bc
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
 
 

1 files changed, 13 insertions, 1 deletions

diff --git a/util/qfloat16-tables/gen_qfloat16_tables.cpp b/util/qfloat16-tables/gen_qfloat16_tables.cpp
index 5aca0235e3..faedb5073c 100644
--- a/util/qfloat16-tables/gen_qfloat16_tables.cpp
+++ b/util/qfloat16-tables/gen_qfloat16_tables.cpp
@@ -41,6 +41,18 @@
 #include <stdint.h>
 #include <stdio.h>
 
+/*
+ * This tool generates the tables used by qfloat16 to implement a
+ * software-emulated version of IEEE 754 binary16. qfloat16 automatically uses
+ * CPU instructions to convert to and from float (IEEE 754 binary32), but if
+ * the CPU is not guaranteed to have those instructions available at compile
+ * time, then qfloat16 needs the tables to perform the conversion with
+ * reasonable performance.
+ *
+ * Because Qt requires float to be IEEE 754 binary32, these tables are
+ * platform-independent and will never change.
+ */
+
 uint32_t convertmantissa(int32_t i)
 {
     uint32_t m = i << 13; // Zero pad mantissa bits
@@ -64,7 +76,7 @@ int main()
 {
     uint32_t i;
 
-    printf("/* This file was generated by gen_qfloat16_tables.cpp */\n\n");
+    printf("/* This file was generated by util/qfloat16-tables/gen_qfloat16_tables.cpp */\n\n");
     printf("#include <QtCore/qfloat16.h>\n\n");
 
     printf("QT_BEGIN_NAMESPACE\n\n");