8000 [Bug #20662] Preserve payloads in packed NaN by nobu · Pull Request #11352 · ruby/ruby · GitHub
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[Bug #20662] Preserve payloads in packed NaN #11352

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[Bug #20662] Preserve payloads in packed NaN #11352

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964d031
[Bug #20662] Preserve payload in packed single-precision NaN
nobu Aug 2, 2024
c5499fc
[Bug #20662] Preserve packed signaling NaN
nobu Aug 8, 2024
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[Bug #20662] Preserve payload in packed single-precision NaN
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@nobu @hsbt
nobu authored and hsbt committed Sep 20, 2024
commit 964d0317132be70d2197b6fd3da739ee679e6640
42 changes: 36 additions & 6 deletions pack.c
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Original file line number Diff line number Diff line change
Expand Up @@ -173,14 +173,44 @@ unknown_directive(const char *mode, char type, VALUE fmt)
mode, unknown, fmt);
}

/* convert float <=> double as IEEE 754-2008, with keeping quiet bit */
static const uint32_t F32_QBIT = (uint32_t)1U << (FLT_MANT_DIG-2);
static const uint64_t F64_QBIT = (uint64_t)1U << (DBL_MANT_DIG-2);
static const uint32_t F32_MANT = ~((uint32_t)~0U << (FLT_MANT_DIG-1));
static const int F64_QBIT_OFFSET = DBL_MANT_DIG - FLT_MANT_DIG;

typedef union {
float f;
double d;
uint32_t u32;
uint64_t u64;
} float_double_conv;

static inline double
unpack_flt2dbl(uint32_t u)
{
float_double_conv tmp = {.u32 = u};
tmp.d = tmp.f;
if (isnan(tmp.d)) {
uint64_t qbit = ((uint64_t)(u & F32_QBIT) << F64_QBIT_OFFSET);
tmp.u64 = (tmp.u64 & ~F64_QBIT) | qbit;
}
return tmp.d;
}

static float
VALUE_to_float(VALUE obj)
{
VALUE v = rb_to_float(obj);
double d = RFLOAT_VALUE(v);

if (isnan(d)) {
return NAN;
float_double_conv tmp = {.d = d};
uint32_t qbit = (uint32_t)((tmp.u64 & F64_QBIT) >> F64_QBIT_OFFSET);
tmp.f = (float)d;
tmp.u32 = (tmp.u32 & ~F32_QBIT) | qbit;
if (!(tmp.u32 & F32_MANT)) tmp.u32 |= 1;
return tmp.f;
}
else if (d < -FLT_MAX) {
return -INFINITY;
Expand Down Expand Up @@ -1291,9 +1321,9 @@ pack_unpack_internal(VALUE str, VALUE fmt, enum unpack_mode mode, long offset)
case 'F':
PACK_LENGTH_ADJUST_SIZE(sizeof(float));
while (len-- > 0) {
float tmp;
UNPACK_FETCH(&tmp, float);
UNPACK_PUSH(DBL2NUM((double)tmp));
FLOAT_CONVWITH(tmp);
UNPACK_FETCH(&tmp.buf, float);
UNPACK_PUSH(DBL2NUM(unpack_flt2dbl(tmp.u)));
}
PACK_ITEM_ADJUST();
break;
Expand All @@ -1304,7 +1334,7 @@ pack_unpack_internal(VALUE str, VALUE fmt, enum unpack_mode mode, long offset)
FLOAT_CONVWITH(tmp);
UNPACK_FETCH(tmp.buf, float);
VTOHF(tmp);
UNPACK_PUSH(DBL2NUM(tmp.f));
UNPACK_PUSH(DBL2NUM(unpack_flt2dbl(tmp.u)));
}
PACK_ITEM_ADJUST();
break;
Expand Down Expand Up @@ -1337,7 +1367,7 @@ pack_unpack_internal(VALUE str, VALUE fmt, enum unpack_mode mode, long offset)
FLOAT_CONVWITH(tmp);
UNPACK_FETCH(tmp.buf, float);
NTOHF(tmp);
UNPACK_PUSH(DBL2NUM(tmp.f));
UNPACK_PUSH(DBL2NUM(unpack_flt2dbl(tmp.u)));
}
PACK_ITEM_ADJUST();
break;
Expand Down
19 changes: 18 additions & 1 deletion test/ruby/test_pack.rb
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Expand Up @@ -532,16 +532,33 @@ def test_pack_unpack_fdeEgG
nan = inf/inf
[0.0, 1.0, 3.0, inf, -inf, nan].each do |x|
%w(f d e E g G).each do |f|
v = [x].pack(f).unpack(f)
packed = [x].pack(f)
v = packed.unpack(f)
if x.nan?
assert_predicate(v.first, :nan?)
assert_equal(packed, v.pack(f))
else
assert_equal([x], v)
end
end
end
end

def test_pack_unpack_float_nan
snan = [0x7fc00000, 0x7fffe000, 0x7fbfe000, 0x7ffff000, 0x7fbff000]
snan.concat(snan.map {|x| 0x80000000 | x}) # negative
snan.each do |x|
msg = "nan(%x)" % x
packed = [x].pack("L")
f = packed.unpack1("f")

assert_predicate(f, :nan?, msg)
assert_equal packed, [f].pack("f"), msg
b64 = [((x & 0xff80_0000) << 32) | 0x70_0000_0000_0000 | ((x & 0x007f_ffff) << 29)].pack("Q")
assert_equal b64, [f].pack("d"), msg
end
end

def test_pack_unpack_x
assert_equal("", [].pack("x0"))
assert_equal("\0", [].pack("x"))
Expand Down
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