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llama2.go
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llama2.go
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package llama2
import (
"bufio"
"encoding/binary"
"fmt"
"io"
"math"
"os"
"sync"
)
type Config struct {
Dim int
HiddenDim int
NLayers int
NHeads int
NKvHeads int
VocabSize int
SeqLen int
}
type Checkpoint interface {
Error() error
Close() error
Dim() int
HiddenDim() int
NLayers() int
NHeads() int
NKvHeads() int
VocabSize() int
SeqLen() int
TokenEmbeddingTable(token int) []float32
RmsAttWeight(layer int) []float32
RmsFfnWeight(layer int) []float32
Wq(layer int) []float32
Wk(layer int) []float32
Wv(layer int) []float32
Wo(layer int) []float32
W1(layer int) []float32
W2(layer int) []float32
W3(layer int) []float32
RmsFinalWeight() []float32
FreqCisReal(pos int) []float32
FreqCisImag(pos int) []float32
Wcls() []float32
}
type RunState struct {
X []float32
Xb []float32
Xb2 []float32
Hb []float32
Hb2 []float32
Q []float32
K []float32
V []float32
Att []float32
Logits []float32
KeyCache []float32
ValueCache []float32
}
type Vocab struct {
strings []string
scores []float32
maxTokenLength int32
}
func (v Vocab) id(s string) int {
for idx, v := range v.strings {
if v == s {
return idx
}
}
return -1
}
func (v Vocab) String(id int) string {
return v.strings[id]
}
func (v Vocab) BPEEncode(text string) ([]int, error) {
tokens := make([]int, 0, v.maxTokenLength)
// first encode every individual byte in the input string
for _, b := range []byte(text) {
id := v.id(string(b))
if id == -1 {
return nil, fmt.Errorf("not good")
}
tokens = append(tokens, id)
}
// merge the best consecutive pair each iteration, according the scores in vocab_scores
for {
bestScore := float32(-1e10)
bestId := -1
bestIdx := -1
for i := 0; i < len(tokens)-1; i++ {
// check if we can merge the pair (tokens[i], tokens[i+1])
id := v.id(v.String(tokens[i]) + v.String(tokens[i+1]))
if id == -1 {
continue
}
if v.scores[id] > bestScore {
bestScore = v.scores[id]
bestId = id
bestIdx = i
}
}
if bestIdx == -1 {
break // we couldn't find any more pairs to merge, so we're done
}
// merge the consecutive pair (best_idx, best_idx+1) into new token best_id
tokens[bestIdx] = bestId
// delete token at position best_idx+1, shift the entire sequence back 1
for i := bestIdx + 1; i < len(tokens)-1; i++ {
tokens[i] = tokens[i+1]
}
tokens = tokens[:len(tokens)-1]
}
return tokens, nil
}
func LoadTokenizer(pathname string, size int) (Vocab, error) {
vocab := Vocab{
strings: make([]string, size),
scores: make([]float32, size),
}
f, err := os.Open(pathname)
if err != nil {
return vocab, fmt.Errorf("loading tokenizer file: %w", err)
}
defer f.Close()
r := bufio.NewReader(f)
if err := binary.Read(r, binary.LittleEndian, &vocab.maxTokenLength); err != nil {
return vocab, fmt.Errorf("reading max token length: %w", err)
}
for i := 0; i < size; i++ {
if err := binary.Read(r, binary.LittleEndian, &vocab.scores[i]); err != nil {
return vocab, fmt.Errorf("reading vocab scores: %w", err)
}
var len int32
if err := binary.Read(r, binary.LittleEndian, &len); err != nil {
return vocab, fmt.Errorf("reading length: %w", err)
}
data := make([]byte, len)
if _, err := io.ReadFull(r, data); err != nil {
return vocab, fmt.Errorf("reading data: %w", err)
}
vocab.strings[i] = string(data)
}
return vocab, nil
}
func NewRunState(c Checkpoint) *RunState {
return &RunState{
X: make([]float32, c.Dim()),
Xb: make([]float32, c.Dim()),
Xb2: make([]float32, c.Dim()),
Hb: make([]float32, c.HiddenDim()),
Hb2: make([]float32, c.HiddenDim()),
Q: make([]float32, c.Dim()),
K: make([]float32, c.Dim()),
V: make([]float32, c.Dim()),
Att: make([]float32, c.NHeads()*c.SeqLen()),
Logits: make([]float32, c.VocabSize()),
KeyCache: make([]float32, c.NLayers()*c.SeqLen()*c.Dim()),
ValueCache: make([]float32, c.NLayers()*c.SeqLen()*c.Dim()),
}
}
func Transformer(token, pos int, c Checkpoint, s *RunState) {
var wg sync.WaitGroup
// copy the token embedding into x
copy(s.X, c.TokenEmbeddingTable(token))
// pluck out the "pos" row of freq_cis_real and freq_cis_imag
freqCisRealRow := c.FreqCisReal(pos)
freqCisImagRow := c.FreqCisImag(pos)
// forward all the layers
headSize := c.Dim() / c.NHeads()
if len(freqCisRealRow) < headSize/2 {
return
}
if len(freqCisImagRow) < headSize/2 {
return
}
for l := 0; l < c.NLayers(); l++ {
// attention rmsnorm
rmsnorm(s.Xb, s.X, c.RmsAttWeight(l))
// qkv matmuls for this position
wg.Add(3)
go func() { matmul(s.Q, s.Xb, c.Wq(l)); wg.Done() }()
go func() { matmul(s.K, s.Xb, c.Wk(l)); wg.Done() }()
go func() { matmul(s.V, s.Xb, c.Wv(l)); wg.Done() }()
wg.Wait()
// apply RoPE rotation to the q and k vectors for each head
for h := 0; h < int(c.NHeads()); h++ {
// get the q and k vectors for this head
q := s.Q[h*headSize:]
k := s.K[h*headSize:]
// rotate q and k by the freq_cis_real and freq_cis_imag
for i := 0; i < headSize; i += 2 {
q0 := q[i]
q1 := q[i+1]
k0 := k[i]
k1 := k[i+1]
fcr := freqCisRealRow[i/2]
fci := freqCisImagRow[i/2]
q[i] = q0*fcr - q1*fci
q[i+1] = q0*fci + q1*fcr
k[i] = k0*fcr - k1*fci
k[i+1] = k0*fci + k1*fcr
}
}
// save key,value at this time step (pos) to our kv cache
loff := l * c.SeqLen() * c.Dim() // kv cache layer offset for convenience
copy(s.KeyCache[loff+pos*c.Dim():], s.K[:c.Dim()])
copy(s.ValueCache[loff+pos*c.Dim():], s.V[:c.Dim()])
// multihead attention. iterate over all heads
wg.Add(c.NHeads())
for h := 0; h < c.NHeads(); h++ {
h := h
go func() {
hhs := h * headSize
// get the query vector for this head
q := s.Q[hhs:]
// attention scores for this head
att := s.Att[h*c.SeqLen():]
// iterate over all timesteps, including the current one
for t := 0; t <= pos; t++ {
// get the key vector for this head and at this timestep
k := s.KeyCache[loff+t*c.Dim()+hhs:]
// calculate the attention score as the dot product of q and k
var score float32
for i := 0; i < headSize; i++ {
score += q[i] * k[i]
}
score /= float32(math.Sqrt(float64(headSize)))
// save the score to the attention buffer
att[t] = score
}
// softmax the scores to get attention weights, from 0..pos inclusively
Softmax(att[:pos+1])
// weighted sum of the values, store back into xb
xb := s.Xb[hhs : hhs+headSize]
for i := range xb {
xb[i] = 0.0
}
for t := 0; t <= pos; t++ {
v := s.ValueCache[loff+t*c.Dim()+hhs : loff+t*c.Dim()+hhs+headSize]
a := att[t]
for i := range v {
xb[i] += a * v[i]
}
}
wg.Done()
}()
}
wg.Wait()
// final matmul to get the output of the attention
matmul(s.Xb2, s.Xb, c.Wo(l))
// residual connection back into x
accum(s.X, s.Xb2)
// ffn rmsnorm
rmsnorm(s.Xb, s.X, c.RmsFfnWeight(l))
wg.Add(2)
go func() { matmul(s.Hb, s.Xb, c.W1(l)); wg.Done() }()
go func() { matmul(s.Hb2, s.Xb, c.W3(l)); wg.Done() }()
wg.Wait()
// F.silu; silu(x)=x*σ(x),where σ(x) is the logistic sigmoid
for i := 0; i < c.HiddenDim(); i++ {
s.Hb[i] = s.Hb[i] * (1.0 / (1.0 + float32(math.Exp(-float64(s.Hb[i])))))
}
// elementwise multiply with w3(x)
for i := 0; i < c.HiddenDim(); i++ {
s.Hb[i] = s.Hb[i] * s.Hb2[i]
}
// final matmul to get the output of the ffn
matmul(s.Xb, s.Hb, c.W2(l))
// residual connection
accum(s.X, s.Xb)
}
// final rmsnorm
rmsnorm(s.X, s.X, c.RmsFinalWeight())
// classifier into logits
matmul(s.Logits, s.X, c.Wcls())
}
func Sample(seed uint64, probabilities []float32) int {
r := randomF32(seed)
var cdf float32
for i, p := range probabilities {
cdf += p
if r < cdf {
return i
}
}
return len(probabilities) - 1
}
func Argmax(v []float32) int {
maxI := 0
maxP := v[0]
for i, p := range v[1:] {
if p > maxP {
maxI = i + 1
maxP = p
}
}
return maxI
}
func Softmax(x []float32) {
maxVal := x[0]
for _, v := range x[1:] {
if v > maxVal {
maxVal = v
}
}
var sum float32
var i int
for ; i < len(x)-4; i += 4 {
x[i] = float32(math.Exp(float64(x[i] - maxVal)))
x[i+1] = float32(math.Exp(float64(x[i+1] - maxVal)))
x[i+2] = float32(math.Exp(float64(x[i+2] - maxVal)))
x[i+3] = float32(math.Exp(float64(x[i+3] - maxVal)))
sum += x[i]
sum += x[i+1]
sum += x[i+2]
sum += x[i+3]
}
for ; i < len(x); i++ {
x[i] = float32(math.Exp(float64(x[i] - maxVal)))
sum += x[i]
}
for i := range x {
x[i] /= sum
}
}
func accum(a, b []float32) {
if len(a) != len(b) {
return
}
var i int
for ; i < len(a)-4; i += 4 {
a[i] += b[i]
a[i+1] += b[i+1]
a[i+2] += b[i+2]
a[i+3] += b[i+3]
}
for ; i < len(a); i++ {
a[i] += b[i]
}
}
func rmsnorm(o, x, weight []float32) {
var ss float32
for _, v := range x {
ss += v * v
}
ss /= float32(len(x))
ss += 1e-5
ss = 1.0 / float32(math.Sqrt(float64(ss)))
if len(x) != len(o) || len(weight) != len(o) {
return
}
for j := range o {
o[j] = weight[j] * ss * x[j]
}
}
func randomU32(seed uint64) uint32 {
// xorshift rng: https://en.wikipedia.org/wiki/Xorshift#xorshift.2A
seed ^= seed >> 12
seed ^= seed << 25
seed ^= seed >> 27
return uint32((seed * 0x2545F4914F6CDD1D) >> 32)
}
func randomF32(seed uint64) float32 { // random float32 in [0,1)
return float32(randomU32(seed)>>8) / 16777216.0
}