On 1/28/26 02:31, Ilya Leoshkevich wrote:
+ FloatParts128 a128, b128, *m128, m128_buf, n128, *q128, q128_buf,
+ r128, *r128_precise;
+ int float_exception_flags = 0;
+ bool is_q128_smallish;
+ uint32_t r_flags;
+ int saved_flags;
+
+ /* Compute precise quotient */
+ parts_float_to_float_widen(&a128, a, status);
+ parts_float_to_float_widen(&b128, b, status);
+ q128_buf = a128;
+ q128 = parts_div(&q128_buf, &b128, status);
Why do you need FloatParts128?
You can see an inexact result from float64 with just FloatParts64.
C.f. soft_f64_div.
+
+ /* Final or partial case? */
+ is_q128_smallish = q128->exp < (fmt->frac_size + 1);
+
+ /*
+ * Final quotient is rounded using final-quotient-rounding method, and
+ * partial quotient is rounded toward zero.
+ *
+ * Rounding of partial quotient may be inexact. This is the whole point
+ * of distinguishing partial quotients, so ignore the exception.
+ */
+ n128 = *q128;
+ saved_flags = status->float_exception_flags;
+ parts_round_to_int(&n128,
+ is_q128_smallish ? final_quotient_rounding_mode :
+ float_round_to_zero,
+ 0, status, &float128_params);
float128_params is definitely wrong. The rounding is supposed to be to the
target format.
+ float_exception_flags = saved_flags;
+ parts_s390_precision_round_normal(&n128, fmt);
parts_round_to_int_normal already takes a rounding mode and frac_size.
It also returns whether or not the rounding was exact.
This appears to be trying to reinvent the wheel.
There's still "... the two integers closest to this precise quotient cannot be both be
represented exactly in the precision of the quotent ..." to contend with. Is that your
"smallish" test? If so, the comment could use some improvement.
+
+ /* Compute precise remainder */
+ m128_buf = b128;
+ m128 = parts_mul(&m128_buf, &n128, status);
+ m128->sign = !m128->sign;
+ status->float_exception_flags = 0;
+ r128_precise = parts_addsub(m128, &a128, status, false);
Surely parts_muladd_scalbn (with scale 0).
r~
