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pack.c: cast from double to float can be undefined

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Generally speaking, a value of double is not always representable
when demoted to a float. ISO C defines what to do when such
conversion loses precision, but leaves it undefined when the
value is completely out of range. (cf: ISO/IEC 9899:1990 section
6.2.1.4).

Because ruby do not have half-precision floating-point types this
is not a frequent headache but for pack / unpack, there are
specifiers that has something to do with C float types.  We have
to explicitly care these situations.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65768 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
shyouhei 2018-11-16 09:04:34 +00:00
parent 3c7852f801
commit ffd9a7ea27
1 changed files with 24 additions and 3 deletions
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27
pack.c
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@ -14,6 +14,7 @@
#include <sys/types.h>
#include <ctype.h>
#include <errno.h>
#include <float.h>
/*
* It is intentional that the condition for natstr is HAVE_TRUE_LONG_LONG
@ -148,6 +149,26 @@ unknown_directive(const char *mode, char type, VALUE fmt)
mode, unknown, fmt);
}
static float
VALUE_to_float(VALUE obj)
{
VALUE v = rb_to_float(obj);
double d = RFLOAT_VALUE(v);
if (isnan(d)) {
return NAN;
}
else if (d < -FLT_MAX) {
return -INFINITY;
}
else if (d <= FLT_MAX) {
return d;
}
else {
return INFINITY;
}
}
/*
* call-seq:
* arr.pack( aTemplateString ) -> aBinaryString
@ -663,7 +684,7 @@ pack_pack(int argc, VALUE *argv, VALUE ary)
float f;
from = NEXTFROM;
f = (float)RFLOAT_VALUE(rb_to_float(from));
f = VALUE_to_float(from);
rb_str_buf_cat(res, (char*)&f, sizeof(float));
}
break;
@ -673,7 +694,7 @@ pack_pack(int argc, VALUE *argv, VALUE ary)
FLOAT_CONVWITH(tmp);
from = NEXTFROM;
tmp.f = (float)RFLOAT_VALUE(rb_to_float(from));
tmp.f = VALUE_to_float(from);
HTOVF(tmp);
rb_str_buf_cat(res, tmp.buf, sizeof(float));
}
@ -704,7 +725,7 @@ pack_pack(int argc, VALUE *argv, VALUE ary)
while (len-- > 0) {
FLOAT_CONVWITH(tmp);
from = NEXTFROM;
tmp.f = (float)RFLOAT_VALUE(rb_to_float(from));
tmp.f = VALUE_to_float(from);
HTONF(tmp);
rb_str_buf_cat(res, tmp.buf, sizeof(float));
}