//go:build amd64

package matmul

import "makarna/pkg/backend/cpu"

const f32NR = 8

// gemvFloat32Range computes out[startN:endN] = aRow * B where:
// - aRow is length K
// - B is NxK row-major (weights)
// - out is length at least endN
//
// It prefers a register-blocked 1x8 micro-kernel on AVX2/AVX-512.
func gemvFloat32Range(out, aRow, b []float32, K, startN, endN int) {
	if startN >= endN {
		return
	}

	if cpu.SupportsAVX512() && K >= 16 {
		gemvFloat32RangeAVX512(out, aRow, b, K, startN, endN)
		return
	}
	if cpu.SupportsAVX2() && K >= 8 {
		gemvFloat32RangeAVX2(out, aRow, b, K, startN, endN)
		return
	}

	bOff := startN * K
	for n := startN; n < endN; n++ {
		out[n] = cpu.DotFloat32(aRow, b[bOff:bOff+K])
		bOff += K
	}
}

func gemvFloat32RangeAVX2(out, aRow, b []float32, K, startN, endN int) {
	kMain := K &^ 7
	if kMain <= 0 {
		bOff := startN * K
		for n := startN; n < endN; n++ {
			out[n] = cpu.DotFloat32(aRow, b[bOff:bOff+K])
			bOff += K
		}
		return
	}

	aTail := aRow[kMain:K]
	kTail := K - kMain

	bOff := startN * K
	n := startN
	for ; n+f32NR <= endN; n += f32NR {
		gemvF32Tile8AVX2(&aRow[0], &b[bOff], &out[n], K)
		if kTail != 0 {
			for t := 0; t < f32NR; t++ {
				rowOff := bOff + t*K + kMain
				var tail float32
				for i := 0; i < kTail; i++ {
					tail += aTail[i] * b[rowOff+i]
				}
				out[n+t] += tail
			}
		}
		bOff += f32NR * K
	}
	for ; n < endN; n++ {
		out[n] = cpu.DotFloat32(aRow, b[bOff:bOff+K])
		bOff += K
	}
}

func gemvFloat32RangeAVX512(out, aRow, b []float32, K, startN, endN int) {
	kMain := K &^ 15
	if kMain <= 0 {
		gemvFloat32RangeAVX2(out, aRow, b, K, startN, endN)
		return
	}

	aTail := aRow[kMain:K]
	kTail := K - kMain

	bOff := startN * K
	n := startN
	for ; n+f32NR <= endN; n += f32NR {
		gemvF32Tile8AVX512(&aRow[0], &b[bOff], &out[n], K)
		if kTail != 0 {
			for t := 0; t < f32NR; t++ {
				rowOff := bOff + t*K + kMain
				var tail float32
				for i := 0; i < kTail; i++ {
					tail += aTail[i] * b[rowOff+i]
				}
				out[n+t] += tail
			}
		}
		bOff += f32NR * K
	}
	for ; n < endN; n++ {
		out[n] = cpu.DotFloat32(aRow, b[bOff:bOff+K])
		bOff += K
	}
}

//go:noescape
func gemvF32Tile8AVX2(a *float32, b *float32, out *float32, K int)

//go:noescape
func gemvF32Tile8AVX512(a *float32, b *float32, out *float32, K int)