quants.py

from __future__ import annotations
from typing import Callable, Sequence

from numpy.typing import DTypeLike

from .constants import GGML_QUANT_SIZES, GGMLQuantizationType
from .lazy import LazyNumpyTensor

import numpy as np


def quant_shape_to_byte_shape(shape: Sequence[int], quant_type: GGMLQuantizationType):
    block_size, type_size = GGML_QUANT_SIZES[quant_type]
    if shape[-1] % block_size != 0:
        raise ValueError(f"Quantized tensor row size ({shape[-1]}) is not a multiple of {quant_type.name} block size ({block_size})")
    return (*shape[:-1], shape[-1] // block_size * type_size)


def quant_shape_from_byte_shape(shape: Sequence[int], quant_type: GGMLQuantizationType):
    block_size, type_size = GGML_QUANT_SIZES[quant_type]
    if shape[-1] % type_size != 0:
        raise ValueError(f"Quantized tensor bytes per row ({shape[-1]}) is not a multiple of {quant_type.name} type size ({type_size})")
    return (*shape[:-1], shape[-1] // type_size * block_size)


# same as ggml_compute_fp32_to_bf16 in ggml-impl.h
def __compute_fp32_to_bf16(n: np.ndarray) -> np.ndarray:
    n = n.astype(np.float32, copy=False).view(np.uint32)
    # force nan to quiet
    n = np.where((n & 0x7fffffff) > 0x7f800000, (n & np.uint32(0xffff0000)) | np.uint32(64 << 16), n)
    # round to nearest even
    n = (np.uint64(n) + (0x7fff + ((n >> 16) & 1))) >> 16
    return n.astype(np.uint16)


# This is faster than np.vectorize and np.apply_along_axis because it works on more than one row at a time
def __apply_over_grouped_rows(func: Callable[[np.ndarray], np.ndarray], arr: np.ndarray, otype: DTypeLike, oshape: tuple[int, ...]) -> np.ndarray:
    rows = arr.reshape((-1, arr.shape[-1]))
    osize = 1
    for dim in oshape:
        osize *= dim
    out = np.empty(shape=osize, dtype=otype)
    # compute over groups of 16 rows (arbitrary, but seems good for performance)
    n_groups = (rows.shape[0] // 16) or 1
    np.concatenate([func(group).ravel() for group in np.array_split(rows, n_groups)], axis=0, out=out)
    return out.reshape(oshape)


def __quantize_bf16_array(n: np.ndarray) -> np.ndarray:
    return __apply_over_grouped_rows(__compute_fp32_to_bf16, arr=n, otype=np.uint16, oshape=n.shape)


__quantize_bf16_lazy = LazyNumpyTensor._wrap_fn(__quantize_bf16_array, meta_noop=np.uint16)


def quantize_bf16(n: np.ndarray):
    if type(n) is LazyNumpyTensor:
        return __quantize_bf16_lazy(n)
    else:
        return __quantize_bf16_array(n)


__q8_block_size, __q8_type_size = GGML_QUANT_SIZES[GGMLQuantizationType.Q8_0]


def can_quantize_to_q8_0(n: np.ndarray) -> bool:
    return n.shape[-1] % __q8_block_size == 0


# round away from zero
# ref: https://stackoverflow.com/a/59143326/22827863
def np_roundf(n: np.ndarray) -> np.ndarray:
    a = abs(n)
    floored = np.floor(a)
    b = floored + np.floor(2 * (a - floored))
    return np.sign(n) * b


def __quantize_q8_0_shape_change(s: tuple[int, ...]) -> tuple[int, ...]:
    return (*s[:-1], s[-1] // __q8_block_size * __q8_type_size)


# Implementation of Q8_0 with bit-exact same results as reference implementation in ggml-quants.c
def __quantize_q8_0_rows(n: np.ndarray) -> np.ndarray:
    shape = n.shape
    assert shape[-1] % __q8_block_size == 0

    n_blocks = n.size // __q8_block_size

    blocks = n.reshape((n_blocks, __q8_block_size)).astype(np.float32, copy=False)

    d = abs(blocks).max(axis=1, keepdims=True) / 127
    with np.errstate(divide="ignore"):
        id = np.where(d == 0, 0, 1 / d)
    qs = np_roundf(blocks * id)

    # (n_blocks, 2)
    d = d.astype(np.float16).view(np.uint8)
    # (n_blocks, block_size)
    qs = qs.astype(np.int8).view(np.uint8)

    assert d.shape[1] + qs.shape[1] == __q8_type_size

    return np.concatenate([d, qs], axis=1).reshape(__quantize_q8_0_shape_change(shape))


def __quantize_q8_0_array(n: np.ndarray) -> np.ndarray:
    return __apply_over_grouped_rows(__quantize_q8_0_rows, arr=n, otype=np.uint8, oshape=__quantize_q8_0_shape_change(n.shape))


__quantize_q8_0_lazy = LazyNumpyTensor._wrap_fn(
    __quantize_q8_0_array,
    meta_noop=(np.uint8, __quantize_q8_0_shape_change),
)


def quantize_q8_0(data: np.ndarray):
    if type(data) is LazyNumpyTensor:
        return __quantize_q8_0_lazy(data)
    else:
        return __quantize_q8_0_array(data)