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authorDimitry Andric <dim@FreeBSD.org>2019-09-28 08:57:29 +0000
committerDimitry Andric <dim@FreeBSD.org>2019-09-28 08:57:29 +0000
commitbc4f7cabbe20fbc3ca6bff0daaca1dcba4bc72ac (patch)
tree8bf6cc290e95f91d4d1477879cbd7fa7e6aaeff1
parent923263dddd270bd3efb79b83c0bea924593747fe (diff)
downloadsrc-bc4f7cabbe20fbc3ca6bff0daaca1dcba4bc72ac.tar.gz
src-bc4f7cabbe20fbc3ca6bff0daaca1dcba4bc72ac.zip
MFC r352710:
Do not left-shift a negative number (inducing undefined behavior in C/C++) in exp(3), expf(3), expm1(3) and expm1f(3) during intermediate computations that compute the IEEE-754 bit pattern for |2**k| for integer |k|. The implementations of exp(3), expf(3), expm1(3) and expm1f(3) need to compute IEEE-754 bit patterns for 2**k in certain places. (k is an integer and 2**k is exactly representable in IEEE-754.) Currently they do things like 0x3FF0'0000+(k<<20), which is to say they take the bit pattern representing 1 and then add directly to the exponent field to get the desired power of two. This is fine when k is non-negative. But when k<0 (and certain classes of input trigger this), this left-shifts a negative number -- an operation with undefined behavior in C and C++. The desired semantics can be achieved by instead adding the possibly-negative k to the IEEE-754 exponent bias to get the desired exponent field, _then_ shifting that into its proper overall position. (Note that in case of s_expm1.c and s_expm1f.c, there are SET_HIGH_WORD and SET_FLOAT_WORD uses further down in each of these files that perform shift operations involving k, but by these points k's range has been restricted to 2 < k <= 56, and the shift operations under those circumstances can't do anything that would be UB.) Submitted by: Jeff Walden, https://github.com/jswalden Obtained from: https://github.com/freebsd/freebsd/pull/411 Obtained from: https://github.com/freebsd/freebsd/pull/412
Notes
Notes: svn path=/stable/8/; revision=352835
-rw-r--r--lib/msun/src/e_exp.c4
-rw-r--r--lib/msun/src/e_expf.c4
-rw-r--r--lib/msun/src/s_expm1.c2
-rw-r--r--lib/msun/src/s_expm1f.c2
4 files changed, 6 insertions, 6 deletions
diff --git a/lib/msun/src/e_exp.c b/lib/msun/src/e_exp.c
index 5b9a10c1a3d6..5403e3756e0c 100644
--- a/lib/msun/src/e_exp.c
+++ b/lib/msun/src/e_exp.c
@@ -143,9 +143,9 @@ __ieee754_exp(double x) /* default IEEE double exp */
/* x is now in primary range */
t = x*x;
if(k >= -1021)
- INSERT_WORDS(twopk,0x3ff00000+(k<<20), 0);
+ INSERT_WORDS(twopk,((u_int32_t)(0x3ff+k))<<20, 0);
else
- INSERT_WORDS(twopk,0x3ff00000+((k+1000)<<20), 0);
+ INSERT_WORDS(twopk,((u_int32_t)(0x3ff+(k+1000)))<<20, 0);
c = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
if(k==0) return one-((x*c)/(c-2.0)-x);
else y = one-((lo-(x*c)/(2.0-c))-hi);
diff --git a/lib/msun/src/e_expf.c b/lib/msun/src/e_expf.c
index 5f4649244f77..f554fd6cdee7 100644
--- a/lib/msun/src/e_expf.c
+++ b/lib/msun/src/e_expf.c
@@ -80,9 +80,9 @@ __ieee754_expf(float x) /* default IEEE double exp */
/* x is now in primary range */
t = x*x;
if(k >= -125)
- SET_FLOAT_WORD(twopk,0x3f800000+(k<<23));
+ SET_FLOAT_WORD(twopk,((u_int32_t)(0x7f+k))<<23);
else
- SET_FLOAT_WORD(twopk,0x3f800000+((k+100)<<23));
+ SET_FLOAT_WORD(twopk,((u_int32_t)(0x7f+(k+100)))<<23);
c = x - t*(P1+t*P2);
if(k==0) return one-((x*c)/(c-(float)2.0)-x);
else y = one-((lo-(x*c)/((float)2.0-c))-hi);
diff --git a/lib/msun/src/s_expm1.c b/lib/msun/src/s_expm1.c
index 3de7bfbc837a..2a030b29c7f4 100644
--- a/lib/msun/src/s_expm1.c
+++ b/lib/msun/src/s_expm1.c
@@ -186,7 +186,7 @@ expm1(double x)
e = hxs*((r1-t)/(6.0 - x*t));
if(k==0) return x - (x*e-hxs); /* c is 0 */
else {
- INSERT_WORDS(twopk,0x3ff00000+(k<<20),0); /* 2^k */
+ INSERT_WORDS(twopk,((u_int32_t)(0x3ff+k))<<20,0); /* 2^k */
e = (x*(e-c)-c);
e -= hxs;
if(k== -1) return 0.5*(x-e)-0.5;
diff --git a/lib/msun/src/s_expm1f.c b/lib/msun/src/s_expm1f.c
index 483472ce69b8..da8f49ddec08 100644
--- a/lib/msun/src/s_expm1f.c
+++ b/lib/msun/src/s_expm1f.c
@@ -92,7 +92,7 @@ expm1f(float x)
e = hxs*((r1-t)/((float)6.0 - x*t));
if(k==0) return x - (x*e-hxs); /* c is 0 */
else {
- SET_FLOAT_WORD(twopk,0x3f800000+(k<<23)); /* 2^k */
+ SET_FLOAT_WORD(twopk,((u_int32_t)(0x7f+k))<<23); /* 2^k */
e = (x*(e-c)-c);
e -= hxs;
if(k== -1) return (float)0.5*(x-e)-(float)0.5;