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fix(sv): read string characters as signed bytes - #2446
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IEEE 1800-2023 6.16 makes a single character of a string variable a `byte`, and 6.16.3 declares `function byte getc(int i)`; 6.11 makes `byte` a signed 2-state type. Celox typed `s[i]` and `s.getc(i)` as unsigned 8-bit values, so a character code above 127 converted to a positive integer. Type them as signed bytes. Impact: a character with code 128..255 now reads as a negative value when it is widened, compared or printed as a number (`int n = s[0]` gives -1 for 8'hff, `s[0] < 0` is true, `%0d` prints -1). ASCII characters, `putc`, assignments of characters to 8-bit variables and string contents are unchanged. The shared string::characters_are_signed_bytes case checks the LRM values. xezim 0.11.3 agrees; Verilator 5.052 and Icarus 13.0 read the code as 255. The Verilator disagreement is retained with a standalone probe, and the case joins Icarus' existing getc limitation. sv-tests conformance is unchanged. Change-Id: I394404abf48a74110753cecf60a1e35952fa5924
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IEEE 1800-2023 6.16 makes a single character of a string variable a
byte,and 6.16.3 declares
function byte getc(int i); 6.11 makesbytea signed2-state type. Celox typed
s[i]ands.getc(i)as unsigned 8-bit values, so acharacter code above 127 converted to a positive integer. Type them as signed
bytes.
Impact: a character with code 128..255 now reads as a negative value when it
is widened, compared or printed as a number (
int n = s[0]gives -1 for 8'hff,s[0] < 0is true,%0dprints -1). ASCII characters,putc, assignments ofcharacters to 8-bit variables and string contents are unchanged.
The shared string::characters_are_signed_bytes case checks the LRM values.
xezim 0.11.3 agrees; Verilator 5.052 and Icarus 13.0 read the code as 255.
The Verilator disagreement is retained with a standalone probe, and the case
joins Icarus' existing getc limitation. sv-tests conformance is unchanged.