From: Adhemerval Zanella Date: Mon, 9 Mar 2026 20:11:12 +0000 (-0300) Subject: math: Add fast-path to fma X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;p=thirdparty%2Fglibc.git math: Add fast-path to fma For normal numbers there is no need to issue scalbn, the fma can set the exponend directly. Performance-wise on x86_64-linux-gnu without multi-arch it shows a latency improvement of ~5% and throughput of %7 (and sligth more for ABIs witht tail-call optimization). Checked on x86_64-linux-gnu and i686-linux-gnu with --disable-multi-arch. Reviewed-by: Wilco Dijkstra --- diff --git a/sysdeps/ieee754/dbl-64/s_fma.c b/sysdeps/ieee754/dbl-64/s_fma.c index d65d505915..88bda86943 100644 --- a/sysdeps/ieee754/dbl-64/s_fma.c +++ b/sysdeps/ieee754/dbl-64/s_fma.c @@ -192,7 +192,10 @@ __fma (double x, double y, double z) i = -i; double r = convertfromint64 (i); /* |r| is in [0x1p62,0x1p63] */ - if (e < -1022 - 62) + if (__glibc_likely (e >= -1084 && e <= 960)) + /* Fast-path for normal numbers. */ + return asdouble (asuint64 (r) + ((int64_t) e << MANTISSA_WIDTH)); + else if (e < -1022 - 62) { /* Result is subnormal before rounding. */ if (e == -1022 - 63)