cconvey commented on code in PR #12340:
URL: https://github.com/apache/tvm/pull/12340#discussion_r948135363
##########
python/tvm/topi/hexagon/utils.py:
##########
@@ -150,4 +157,126 @@ def get_layout_transform_fn(layout):
return nc_2048_2d
if layout == "nhwc-8h8w32c-2d":
return nhwc_8h8w32c_2d
+ if layout == "n11c-2048c-2d":
+ return n11c_2048c_2d
raise RuntimeError(f"Unexpected layout '{layout}'")
+
+
+def get_fixed_point_value(flp: float, dtype: str = "int16"):
+ """
+ Return fixed-point value and the corresponding log2 of the scale factor
used to compute
+ this value.
+
+ Parameters
+ ----------
+ flp : float
+ Floating-point value to be converted
+ dtype : str
+ Type of the resulting fixed-point value. By default, it's set to
"int16"
+
+ Returns
+ -------
+ fixed_point_value : int
+ Fixed-point value for the given floating-point value
+ exp_scale_factor : int
+ log2 of the scale factor
+
+ Convert floating-point value into fixed-point number. This is done by
+ multiplying the value by a scaling factor and then rounding it to the
nearest
+ integer value.
+
+ As per IEEE-754 standard, a floating-point value can be represented as
follows
+ [see: https://en.wikipedia.org/wiki/IEEE_754-1985]:
+ (-1)^S * M * 2^(E-Bias)
+
+ Here,
+ * S is the signed bit (0 or 1).
+ * M is the mantissa. It's composed of an implicit 1 for the normalized
floating-point
+ values or 0 for the denormalized values, and the fraction part. This
ensures that
+ mantissa is always within [0, 2) range. Please note that this function
doesn't
+ handle denormalized values.
+ * E is the exponent.
+
+ In single precision, 23 bits are used to represent the fraction part of
+ the mantissa (and therefore, '23' shows up in one of the computations
below) and
+ 8 bits are used for the exponent. Since exponent field needs to reperesent
both
+ positive and negative values, a bias (127 for single precision) is added
to the actual
+ value. Therefore, to compute the actual exponent, 127 must be subtracted
from the stored
+ value.
+
+ As mentioned above, to find the corresponding fixed-point number, we
multiply the
+ value with a scaling factor and then round it to the nearest integer. The
scaling factor
+ is chosen to be a power for 2 and it's the largest value that can be
safely multiplied
+ to the floating-point value, without causing the resulting value to
overflow the range
+ of the integer type used to represent the fixed-point value.
+
+ So, if we assume the scaling factor to be 2^x, the resulting fixed-point
value will be:
+ round((-1)^S * (M) * 2^(E-Bias) * 2^x)
+
+ This can be simplified to:
+ round((-1)^S * M * 2^(E-Bias+x)
+
+ Now, if 'int16' is used for fixed-point value, then it has to be >= -(2 *
2^14)
+ and <= (2 * 2^14) - 1. Since M (Mantissa) is always < 2, in order for the
fixed-point value
+ to be within this range, 2^(E - Bias + x) must be <= 2^14 - 1.
+ And, if we ignore -1, (E - Bias + x) should be <= 14. Note: if mantissa
gets too close to 2,
+ this will cause the resulting value to go out of range and require it to
be saturated.
+ In the following implementation, we perform range check and adjust the
scale to avoid
+ saturation.
+ For most cases, 2^x, where x = 14 - (E - Bias) or 14 - (E - 127) for
single precision, is the
+ best scaling factor for 'int16' type that can be used to convert the
floating-point value to
+ fixed-point with the least amount of precision loss.
+
+ Additonal notes on various floating-point values:
+ ------------------------------------------------
+ 1) Denormalized values: Can't be represented as fixed-point - causes
assertion failure
Review Comment:
I'm confused by the claim that denormal values can't be expressed as
fixed-point.
My understanding is that IEEE-754 denormalized format is simply a special
way of encoding numbers that are much closer to 0 than normalized float16
values can express. I don't understand why that's fundamentally inexpressable
as fixed-point.
Are we assuming some additional unstated limitations on our fixedpoint
representation? E.g., the range of values that we're willing to let `rsh` take
on?
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