endianmacros: Replace borked PA_FLOAT32_SWAP() with PA_READ_FLOAT32RE() / PA_WRITE_FLOAT32RE()

building PA with -O0 leads to test failure in mix-test on i386

issue reported by Felipe, see
http://lists.freedesktop.org/archives/pulseaudio-discuss/2014-August/021406.html

the problem is the value 0xbeffbd7f: when byte-swapped it becomes 0x7fbdffbe and according
to IEEE-754 represents a signalling NaN (starting with s111 1111 10, see http://en.wikipedia.org/wiki/NaN)

when this value is assigned to a floating point register, it becomes 0x7ffdffbe, representing
a quiet NaN (starting with s111 1111 11) -- a signalling NaN is turned into a quiet NaN!

so PA_FLOAT32_SWAP(PA_FLOAT32_SWAP(x)) != x for certain values, uhuh!

the following test code can be used; due to volatile, it will always demonstrate the issue;
without volatile, it depends on the optimization level (i386, 32-bit, gcc 4.9):

// snip

static inline float PA_FLOAT32_SWAP(float x) {
    union {
        float f;
        uint32_t u;
    } t;

    t.f = x;
    t.u = bswap_32(t.u);
    return t.f;
}

int main() {
  unsigned x = 0xbeffbd7f;
  volatile float f = PA_FLOAT32_SWAP(*(float *)&x);
  printf("%08x %08x %08x %f\n", 0xbeffbd7f, *(unsigned *)&f, bswap_32(*(unsigned *)&f), f);
}
// snip

the problem goes away with optimization when no temporary floating point registers are used

the proposed solution is to avoid passing swapped floating point data in a
float; this is done with new functions PA_READ_FLOAT32RE() and PA_WRITE_FLOAT32RE()
which use uint32_t to dereference a pointer and byte-swap the data, hence no temporary
float variable is used

also delete PA_FLOAT32_TO_LE()/_BE(), not used

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reported-by: Felipe Sateler <fsateler@debian.org>

2 files changed, 4 insertions, 4 deletions

diff --git a/src/tests/mix-test.c b/src/tests/mix-test.c
index d5bae13ed..e95607dee 100644
--- a/src/tests/mix-test.c
+++ b/src/tests/mix-test.c
@@ -150,7 +150,7 @@ static void compare_block(const pa_sample_spec *ss, const pa_memchunk *chunk, in
             float *u = d;
 
             for (i = 0; i < chunk->length / pa_frame_size(ss); i++) {
-                float uu = PA_MAYBE_FLOAT32_SWAP(ss->format != PA_SAMPLE_FLOAT32NE, *u);
+                float uu = ss->format == PA_SAMPLE_FLOAT32NE ? *u : PA_READ_FLOAT32RE(u);
                 fail_unless(fabsf(uu - *v) <= 1e-6f, NULL);
                 ++u;
                 ++v;
@@ -264,7 +264,7 @@ static pa_memblock* generate_block(pa_mempool *pool, const pa_sample_spec *ss) {
             if (ss->format == PA_SAMPLE_FLOAT32RE) {
                 float *u = d;
                 for (i = 0; i < 10; i++)
-                    u[i] = PA_FLOAT32_SWAP(float32ne_result[0][i]);
+                    PA_WRITE_FLOAT32RE(&u[i], float32ne_result[0][i]);
             } else
                 memcpy(d, float32ne_result[0], sizeof(float32ne_result[0]));
 
diff --git a/src/tests/resampler-test.c b/src/tests/resampler-test.c
index 60345afb3..f547770b8 100644
--- a/src/tests/resampler-test.c
+++ b/src/tests/resampler-test.c
@@ -98,7 +98,7 @@ static void dump_block(const char *label, const pa_sample_spec *ss, const pa_mem
             float *u = d;
 
             for (i = 0; i < chunk->length / pa_frame_size(ss); i++) {
-                printf("%4.3g ", ss->format == PA_SAMPLE_FLOAT32NE ? *u : PA_FLOAT32_SWAP(*u));
+                printf("%4.3g ", ss->format == PA_SAMPLE_FLOAT32NE ? *u : PA_READ_FLOAT32RE(u));
                 u++;
             }
 
@@ -222,7 +222,7 @@ static pa_memblock* generate_block(pa_mempool *pool, const pa_sample_spec *ss) {
 
             if (ss->format == PA_SAMPLE_FLOAT32RE)
                 for (i = 0; i < 10; i++)
-                    u[i] = PA_FLOAT32_SWAP(u[i]);
+                    PA_WRITE_FLOAT32RE(&u[i], u[i]);
 
             break;
         }