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int3-g64 (fmt=5): per-group-scale 3-bit weight format — engine, converter, tests

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New weight format: int3 with ONE f32 scale per 64-input group (3.5 bits/weight
effective). Per group: 16B low plane (2 bits/val, int2 layout) + 8B high plane
(1 bit/val), values [-4,3] stored v+4. Same quantization math as
tools/quant_ablation.py _quant_last_dim(bits=3, group=64) from #132, whose
OLMoE ablation measured int3-g64 BEATING the shipped per-row int4 on quality
(-7.5 vs -9.3pp) at ~14% fewer bits.

Engine (placed per the #391 split): matmul_i3 + pack_int3_g64 + I3_* layout
helpers in quant.h next to their kernel family; fmt=5 branches in colibri.c's
qt_bytes/qt_alloc/qt_fill/matmul_qt/embed_row/qt_addrow/qt_matvec_rows.

Format detection now goes through #413's qt_resolve_fmt: fmt=5 registers its
distinct weight-byte layout O*ceil(I/64)*24 and its scale cardinality
O*ceil(I/64) there, validated against [O,I] like every other format. int3-g64
and grouped-int4-at-gs=64 carry the SAME scale count, so the weight bytes are
the int3 tag; row formats keep precedence for the small-I shapes where byte
counts coincide. The io_uring expert path still used the raw ?1:?2:3 byte
inference (it missed fmt=4 grouping entirely and never set gs) — converted to
qt_resolve_fmt like the other two expert paths.

Backends: qt_cuda_upload returns 0 for fmt=5 (tensor stays CPU-side, the
documented fallback), the dense CUDA matmul gate excludes fmt=5, and Metal's
existing fmt gates (gemm fmt<=3, moe fmt 1/2) already reject it.

Converter: quant_int3_g64 in convert_fp8_to_int4.py; --ebits 3/--xbits 3 now
emit it (previously bits=3 silently produced int4).

Tests: tests/test_int3.c (bit-exact pack/unpack vs reference, matmul_i3 vs
dequant-matmul incl. short tail groups and the real GLM I=7168, QT plumbing,
qt_resolve_fmt disambiguation incl. the same-scale-count fmt=4/fmt=5 pair,
outlier-rows RMS: int3-g64 3.3x lower error than per-row int4),
tests/test_int3_load.c (hand-rolled .safetensors fixture through st_init +
qt_from_disk: fmt=5 detected and loaded next to an int4 control tensor),
tests/test_int3_convert.py (NumPy pack round-trip vs independent decoder).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
FABIOTESS
2026-07-20 17:31:05 +01:00
parent ebd85a781b
commit 5e42e70ec3
7 changed files with 503 additions and 12 deletions
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c/Makefile
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@@ -171,7 +171,7 @@ else
PYTHON ?= python3
endif
CUDA_OBJ =
TEST_BINS = tests/test_json$(EXE) tests/test_st$(EXE) tests/test_st_pread$(EXE) tests/test_tier$(EXE) tests/test_grammar$(EXE) tests/test_schema_gbnf$(EXE) tests/test_decode_batch$(EXE) tests/test_idot$(EXE) tests/test_i4_grouped$(EXE) tests/test_stops$(EXE) tests/test_topp$(EXE) tests/test_sample_nan$(EXE) tests/test_tok_o200k$(EXE) tests/test_kv_alloc$(EXE) tests/test_i4_acc512$(EXE) tests/test_compat_direct$(EXE) tests/test_dsa_select$(EXE) tests/test_logit_nan$(EXE) tests/test_pipe_block$(EXE)
TEST_BINS = tests/test_json$(EXE) tests/test_st$(EXE) tests/test_st_pread$(EXE) tests/test_tier$(EXE) tests/test_grammar$(EXE) tests/test_schema_gbnf$(EXE) tests/test_decode_batch$(EXE) tests/test_idot$(EXE) tests/test_i4_grouped$(EXE) tests/test_stops$(EXE) tests/test_topp$(EXE) tests/test_sample_nan$(EXE) tests/test_tok_o200k$(EXE) tests/test_kv_alloc$(EXE) tests/test_int3$(EXE) tests/test_int3_load$(EXE) tests/test_i4_acc512$(EXE) tests/test_compat_direct$(EXE) tests/test_dsa_select$(EXE) tests/test_logit_nan$(EXE) tests/test_pipe_block$(EXE)
ifneq (,$(LINUX))
TEST_BINS += tests/test_uring$(EXE)
endif
@@ -343,6 +343,12 @@ tests/test_sample_nan$(EXE): tests/test_sample_nan.c colibri.c st.h uring.h json
tests/test_kv_alloc$(EXE): tests/test_kv_alloc.c colibri.c st.h json.h tok.h tok_unicode.h compat.h grammar.h tier.h quant.h sample.h kv_persist.h telemetry.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
tests/test_int3$(EXE): tests/test_int3.c colibri.c st.h uring.h json.h tok.h tok_unicode.h compat.h grammar.h tier.h quant.h sample.h kv_persist.h telemetry.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
tests/test_int3_load$(EXE): tests/test_int3_load.c colibri.c st.h uring.h json.h tok.h tok_unicode.h compat.h grammar.h tier.h quant.h sample.h kv_persist.h telemetry.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
tests/test_logit_nan$(EXE): tests/test_logit_nan.c colibri.c st.h uring.h json.h tok.h tok_unicode.h compat.h grammar.h tier.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)