[m-rev.] diff: broken generic string_to_float

[Peter Wang]

Branches: main, 11.01

library/string.m:
        Revert a bad change to the generic implementation of
        `string.float_to_string' intended to trim redundant trailing zeros.
        However, it also trimmed digits from the exponent!
        e.g. "1e-10" to "1e-1"

        (C, C# and Java backends have their own foreign_procs)

diff --git a/library/string.m b/library/string.m
index 8ab5454..1f25dc8 100644
--- a/library/string.m
+++ b/library/string.m
@@ -3658,7 +3658,7 @@ string.float_to_string(Float, unsafe_promise_unique(String)) :-
     % XXX The unsafe_promise_unique is needed because in
     % string.float_to_string_2 the call to string.to_float doesn't
     % have a (ui, out) mode hence the output string cannot be unique.
-    String = trim_float_string(string.float_to_string_2(min_precision, Float)).
+    String = string.float_to_string_2(min_precision, Float).
 
 :- func string.float_to_string_2(int, float) = (string) is det.
 
@@ -3858,34 +3858,6 @@ string.det_to_float(FloatString) =
     end
 ").
 
-    % Trim redundant trailing zeroes from the fractional part of the
-    % string representation of a float.
-    %
-:- func trim_float_string(string) = string.
-
-trim_float_string(FloatStr0) = FloatStr :-
-    L = string.length(FloatStr0),
-    N = count_extra_trailing_zeroes(FloatStr0, L - 1, 0),
-    FloatStr = string.left(FloatStr0, L - N).
-
-:- func count_extra_trailing_zeroes(string, int, int) = int.
-
-count_extra_trailing_zeroes(FloatStr, I, N0) = N :-
-    ( if I < 0 then
-        N = N0
-      else
-        C = FloatStr ^ elem(I),
-        ( if C = ('0') then
-            N = count_extra_trailing_zeroes(FloatStr, I - 1, N0 + 1)
-          else if C = ('.') then
-            N = int.max(N0 - 1, 0)
-          else if char.is_digit(C) then
-            N = N0
-          else
-            N = 0
-        )
-    ).
-
 /*-----------------------------------------------------------------------*/
 
     % strchr always returns true when searching for '\0',

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