Package: libc6 Version: 2.19-18+deb8u7 Severity: normal Tags: jessie The following C program produces different output on Jessie and Sid. I believe the Sid output is the correct one, and in fact this is the output that has been observed for the "point" (and "polygon") regression tests for PostgreSQL on all platforms for the last 20 years since the test got added.
$ cat sqrt.c #include <math.h> #include <stdio.h> #include <fenv.h> double pg_hypot(double x, double y) { double yx; /* Some PG-specific code deleted here */ /* Else, drop any minus signs */ x = fabs(x); y = fabs(y); /* Swap x and y if needed to make x the larger one */ if (x < y) { double temp = x; x = y; y = temp; } /* * If y is zero, the hypotenuse is x. This test saves a few cycles in * such cases, but more importantly it also protects against * divide-by-zero errors, since now x >= y. */ if (y == 0.0) return x; /* Determine the hypotenuse */ yx = y / x; return x * sqrt(1.0 + (yx * yx)); } int main () { //fesetround(FE_TONEAREST); printf("fegetround is %d\n", fegetround()); double r = pg_hypot(10.0, 10.0); printf("14 %.14g\n", r); printf("15 %.15g\n", r); printf("16 %.16g\n", r); printf("17 %.17g\n", r); return 0; } Jessie output: fegetround is 0 14 14.142135623731 15 14.1421356237309 16 14.14213562373095 17 14.142135623730949 Sid output: fegetround is 0 14 14.142135623731 15 14.142135623731 16 14.14213562373095 17 14.142135623730951 The Sid output is also observed when running the binary compiled on Jessie on Sid, so it's a library issue, not a compiler/binary one. The problem might be due to the fix for #843904. FTBFS in postgresql-9.4 in jessie-pu: https://buildd.debian.org/status/fetch.php?pkg=postgresql-9.4&arch=powerpc&ver=9.4.11-0%2Bdeb8u1&stamp=1487473754&raw=0 FTBFS in postgresql-9.6 in jessie-backports: https://buildd.debian.org/status/fetch.php?pkg=postgresql-9.6&arch=powerpc&ver=9.6.1-2~bpo8%2B1&stamp=1485184696&raw=0 Thread on pgsql-hackers: https://www.postgresql.org/message-id/20170220155819.m2s43pf2pvkes4pc%40msg.credativ.de Christoph
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