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stepcompress: Check for small negative numbers on sqrt() calls 

It's theoretically possible for floating point truncation to cause a
math formula to return a small negative number instead of 0.  If
sqrt() is called on this small negative number it could cause a
crash.  Check for this case and return 0.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2016-10-09 20:57:55 -04:00
parent 9fa0a62c8a
commit ab54fcd443
1 changed files with 13 additions and 2 deletions
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15
klippy/stepcompress.c
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@ -249,6 +249,17 @@ check_line(struct stepcompress *sc, struct step_move move)
* Step compress interface
****************************************************************/
// Wrapper around sqrt() to handle small negative numbers
static inline double
safe_sqrt(double v)
{
if (v < 0. && v > -0.001)
// Due to floating point truncation, it's possible to get a
// small negative number - treat it as zero.
return 0.;
return sqrt(v);
}
// Allocate a new 'stepcompress' object
struct stepcompress *
stepcompress_alloc(uint32_t max_error, uint32_t queue_step_msgid, uint32_t oid)
@ -325,12 +336,12 @@ stepcompress_push_sqrt(struct stepcompress *sc, double steps, double step_offset
double pos = step_offset + sqrt_offset/factor;
if (factor >= 0.0)
while (qn < end) {
*qn++ = clock_offset + sqrt(pos*factor);
*qn++ = clock_offset + safe_sqrt(pos*factor);
pos += 1.0;
}
else
while (qn < end) {
*qn++ = clock_offset - sqrt(pos*factor);
*qn++ = clock_offset - safe_sqrt(pos*factor);
pos += 1.0;
}
sc->queue_next = qn;