URL:
<http://savannah.nongnu.org/bugs/?41435>
Summary: math library functions in uril/delay.h
Project: AVR C Runtime Library
Submitted by: raphendyr
Submitted on: Sun 02 Feb 2014 04:13:34 PM GMT
Category: Header
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: Header files
Status: None
Percent Complete: 0%
Assigned to: None
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Release: Unknown
Fixed Release: None
_______________________________________________________
Details:
New version of _delay_ms (the one using __builtin_avr_delay_cycles) uses math
functions fabs and ceil.
Code expects that when run on hosted and optimized compilation these calls are
optimized away. As this is impossible in freestanding environment there is
macro test (__STDC_HOSTED__) and code fallback to old code.
This is kind of ok, but there is possibility to make this otherwise.
Following code works in freestanding environment:
```
static void _delay_ms(double ms) __attribute__ ((unused));
static void _delay_ms(double ms) {
extern void __builtin_avr_delay_cycles(unsigned long);
extern double __builtin_fabs(double);
extern double __builtin_ceil(double);
double tmp = ((F_CPU) / 1e3) * ms;
uint32_t ticks_dc = (uint32_t)(__builtin_ceil(__builtin_fabs(tmp)));
__builtin_avr_delay_cycles(ticks_dc);
}
```
As we can see from above, we could use __builtin_fabs and __builtin_ceil in
delay.h instead of expecting the compiler to use them.
I think this is better as we already use __buildin_avr_delay_cycles which
requires build time constant argument, thus we can use __builtin_fabs and
__builtin_ceil as we know their arguments are built time constant.
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