stillwater-sc / universal / 35746543765

87%

master: 84%

Build Type

push

github

Committed by web-flow

Commit Message

fix(dbns): implement the efloat/ereal manipulators, correct dbns scale, detect the format surface (#1584)

* fix(dbns): implement the efloat/ereal manipulators, correct dbns scale, detect the format surface

Four defects, all of them things that compiled and so went unnoticed.

1. efloat and ereal manipulator placeholders

to_hex, hex_print, pretty_print and color_print each returned the literal
string "tbd" in both headers -- eight functions. to_hex and hex_print carried
commented-out bodies that indexed a nibble(n) and an nbits neither type has.

Both are now rendered the way the library already renders multi-component
values: dd delegates to its limbs' native color_print and joins them, qd labels
each component, dd_cascade tags the type and joins. The two elastic types split
on what their limbs are. An ereal's limbs ARE floating-point values, so it
delegates to the native renderings exactly as dd does. An efloat's limbs are
uint32_t magnitude words with a separate exponent, so there is nothing to
delegate to and it renders the words itself, the way its working to_binary
already did.

2. dbns::scale() reported the wrong scale for almost every encoding

It computed e0 + e1*log2(3). A dbns encodes (-1)^s * base0^e0 * base1^e1 with
base0 = 0.5, so the base-0.5 exponent contributes NEGATIVELY and the scale is
-e0 + e1*log2(3). It answered 2 for 1.5, whose scale is 0, and +1 for 0.5,
whose scale is -1. Sweeping all 256 encodings of dbns<8,3> against
floor(log2(|v|)), 224 of them were wrong.

The type already knew better everywhere else. operator< documents the value as
(-1)^s * 0.5^a * 3^b and orders on M(x) = -a + b*log2of3; convert_ieee754 says
"in our representation we have 0.5^a * 3^b, which would be equivalent to a
being negative" and only accepts a <= 0, storing its magnitude. scale() was the
one place that disagreed.

Two further defects in the same function: zero returned 7 rather than 0, and
the static_cast truncated toward zero where a scale mu... (continued)

Coverage Stats

94 of 101 new or added lines in 5 files covered. (93.07%)

11 existing lines in 3 files now uncovered.

45424 of 52876 relevant lines covered (85.91%)

9269145.78 hits per line