test: add valid positive and negative J-type immediate encoding tests to encoder#606
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amathxbt wants to merge 1 commit into
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test: add valid positive and negative J-type immediate encoding tests to encoder#606amathxbt wants to merge 1 commit into
amathxbt wants to merge 1 commit into
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test_j_type_jump_boundaries previously used 1048576 (2^20) as both "positive" and "negative" 1 MB jumps. Because 2^20 equals the minimum value in a 21-bit two's-complement immediate field, both op_c values produce the same 32-bit encoding (0x800000EF), so the test did not exercise the encoder's handling of any valid negative offset. Replace the ambiguous test cases with: - JAL x1, +16 (valid positive) -> 0x10000EF - JAL x1, -8 (valid negative) -> 0xFF9FF0EF The expected values are derived from the RISC-V J-type bit-field layout and confirmed manually. The original ±1 MB case is retained with a comment explaining the two's-complement identity.
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Problem
test_j_type_jump_boundariesusesop_c = 1048576(2^20) for the “positive” case andop_c = -1048576i32 as u32for the “negative” case, then asserts both produce0x800000EF.This is not a sign error — it is a two’s-complement identity: 2^20 equals the minimum representable value in a 21-bit signed immediate field (the J-type field width), so the two
op_cvalues are bit-for-bit identical. The test never exercises any valid negative jump offset, leaving the encoder’s negative-immediate path entirely untested.The B-type test (
test_b_type_branch_offsets) correctly tests a negative offset (BEQ x1, x2, -16); the J-type test should do the same.Fix
Add two concrete test cases that cover valid positive and negative J-type immediates:
JAL x1, +160x10000EFJAL x1, -8-8i32 as u320xFF9FF0EFExpected values are derived from the RISC-V J-type bit-field layout (spec §2.5) and verified manually. The original ±1 MB case is retained with a comment explaining the two’s-complement identity.