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

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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>
This commit is contained in:
Peter Meerwald 2014-09-02 23:53:09 +02:00
parent 5d7b5e509c
commit 293a1739e2
7 changed files with 32 additions and 40 deletions
Download patch file Download diff file Expand all files Collapse all files

23
src/pulsecore/endianmacros.h
View file

@ -71,15 +71,24 @@ static inline void PA_WRITE24LE(uint8_t *p, uint32_t u) {
p[0] = (uint8_t) u;
}
static inline float PA_FLOAT32_SWAP(float x) {
static inline float PA_READ_FLOAT32RE(const void *p) {
union {
float f;
uint32_t u;
} t;
t.u = PA_UINT32_SWAP(*(uint32_t *) p);
return t.f;
}
static inline void PA_WRITE_FLOAT32RE(void *p, float x) {
union {
float f;
uint32_t u;
} t;
t.f = x;
t.u = PA_UINT32_SWAP(t.u);
return t.f;
*(uint32_t *) p = PA_UINT32_SWAP(t.u);
}
#define PA_MAYBE_INT16_SWAP(c,x) ((c) ? PA_INT16_SWAP(x) : (x))
@ -88,8 +97,6 @@ static inline float PA_FLOAT32_SWAP(float x) {
#define PA_MAYBE_INT32_SWAP(c,x) ((c) ? PA_INT32_SWAP(x) : (x))
#define PA_MAYBE_UINT32_SWAP(c,x) ((c) ? PA_UINT32_SWAP(x) : (x))
#define PA_MAYBE_FLOAT32_SWAP(c,x) ((c) ? PA_FLOAT32_SWAP(x) : (x))
#ifdef WORDS_BIGENDIAN
#define PA_INT16_FROM_LE(x) PA_INT16_SWAP(x)
#define PA_INT16_FROM_BE(x) ((int16_t)(x))
@ -115,9 +122,6 @@ static inline float PA_FLOAT32_SWAP(float x) {
#define PA_UINT32_TO_LE(x) PA_UINT32_SWAP(x)
#define PA_UINT32_TO_BE(x) ((uint32_t)(x))
#define PA_FLOAT32_TO_LE(x) PA_FLOAT32_SWAP(x)
#define PA_FLOAT32_TO_BE(x) ((float) (x))
#define PA_READ24NE(x) PA_READ24BE(x)
#define PA_WRITE24NE(x,y) PA_WRITE24BE((x),(y))
@ -148,9 +152,6 @@ static inline float PA_FLOAT32_SWAP(float x) {
#define PA_UINT32_TO_LE(x) ((uint32_t)(x))
#define PA_UINT32_TO_BE(x) PA_UINT32_SWAP(x)
#define PA_FLOAT32_TO_LE(x) ((float) (x))
#define PA_FLOAT32_TO_BE(x) PA_FLOAT32_SWAP(x)
#define PA_READ24NE(x) PA_READ24LE(x)
#define PA_WRITE24NE(x,y) PA_WRITE24LE((x),(y))