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gen_qfloat16_tables: add a comment explaining what the tool is

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For our future selves.

Change-Id: I2b1955a995ad40f3b89afffd15a4c127686662bc
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Thiago Macieira 2019-06-03 10:42:25 -07:00
parent 5e40d3d982
commit 041a5ff076
1 changed files with 13 additions and 1 deletions
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14
util/qfloat16-tables/gen_qfloat16_tables.cpp
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@ -41,6 +41,18 @@
#include <stdint.h> #include <stdint.h>
#include <stdio.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 convertmantissa(int32_t i)
{ {
uint32_t m = i << 13; // Zero pad mantissa bits uint32_t m = i << 13; // Zero pad mantissa bits
@ -64,7 +76,7 @@ int main()
{ {
uint32_t i; 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("#include <QtCore/qfloat16.h>\n\n");
printf("QT_BEGIN_NAMESPACE\n\n"); printf("QT_BEGIN_NAMESPACE\n\n");