[linuxdc-dev]Floating point problems - Dreamcast 2.4.10-pre6 kernel

[Adrian M. <ad...@mc...>]

I have been working to make/port a decent mp3 player for the Dreamcast now 
that there is a sound driver.

I have built mpg123 with these options:

dream:
	$(MAKE) CC=sh4-linux-gcc LDFLAGS= \
	OBJECTS='decode.o dct64.o audio_oss.o' \
	CFLAGS='-DREAL_IS_FLOAT -DLINUX -Wall -O2 \
		-DOSS \
		-fomit-frame-pointer -funroll-all-loops \
		-finline-functions -ffast-math' \
		mpg123-make

but this always generates a floating point exception at run time.

I have been able to isolate this to the following function:

costab[k] = 1.0 / (2.0 * cos( 3.14159265358979323846 * ((double) k * 2.0 + 
1.0) / (double) divv));

This is looped 0 < k < kr With k as 0 it costab[k] is returned as NaN and 
with k = 1 the floating point exception is generated. kr is 16 and divv is 64.

My maths indicates costab[0] should be roughly 0.5.

Incuidentally with -DREAL_IS_FLOAT switched off then there is no fp exception 
but the program outputs static.

So: the questions are - is this a known problem, has it been fixed in later 
kernels or have I just got it wrong?


Adrian