From: Joseph Myers <jos...@codesourcery.com> On overflow, the math-emu macro _FP_TO_INT_ROUND tries to saturate its result (subject to the value of rsigned specifying the desired overflow semantics). However, if the rounding step has the effect of increasing the exponent so as to cause overflow (if the rounded result is 1 larger than the largest positive value with the given number of bits, allowing for signedness), the overflow does not get detected, meaning that for unsigned results 0 is produced instead of the maximum unsigned integer with the give number of bits, without an exception being raised for overflow, and that for signed results the minimum (negative) value is produced instead of the maximum (positive) value, again without an exception. This patch makes the code check for rounding increasing the exponent and adjusts the exponent value as needed for the overflow check.
Signed-off-by: Joseph Myers <jos...@codesourcery.com> --- This macro is not present in the glibc/libgcc version of the code. This patch is independent of my separate patch <http://lkml.org/lkml/2013/10/8/694> to fix the results for unsigned saturation, although you need both patches together to get the correct results for the affected unsigned overflow case. It remains the case both before and after this patch that the conversions wrongly treat a signed result of the most negative integer as an overflow, when actually only that integer minus 1 or smaller should be an overflow, although this only means an incorrect exception rather than affecting the value returned; that was one of the bugs I fixed in the glibc/libgcc version of this code in 2006 (as part of a major overhaul of the code including various interface changes, so not trivially backportable to the kernel version). diff --git a/include/math-emu/op-common.h b/include/math-emu/op-common.h index 9696a5e..6bdf8c6 100644 --- a/include/math-emu/op-common.h +++ b/include/math-emu/op-common.h @@ -743,12 +743,17 @@ do { \ } \ else \ { \ + int _lz0, _lz1; \ if (X##_e <= -_FP_WORKBITS - 1) \ _FP_FRAC_SET_##wc(X, _FP_MINFRAC_##wc); \ else \ _FP_FRAC_SRS_##wc(X, _FP_FRACBITS_##fs - 1 - X##_e, \ _FP_WFRACBITS_##fs); \ + _FP_FRAC_CLZ_##wc(_lz0, X); \ _FP_ROUND(wc, X); \ + _FP_FRAC_CLZ_##wc(_lz1, X); \ + if (_lz1 < _lz0) \ + X##_e++; /* For overflow detection. */ \ _FP_FRAC_SRL_##wc(X, _FP_WORKBITS); \ _FP_FRAC_ASSEMBLE_##wc(r, X, rsize); \ } \ -- Joseph S. Myers jos...@codesourcery.com _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
