5bit quants (#2226)

* 5bit quants

* 5bit quants

mlx/backend/cpu/quantized.cpp

@@ -13,9 +13,18 @@ namespace mlx::core {
 
 namespace {
 
+inline constexpr short get_pack_factor(int bits, int wsize = 8) {
+  return (bits == 3 || bits == 5) ? 8 : (bits == 6 ? 4 : wsize / bits);
+}
+
+inline constexpr short get_bytes_per_pack(int bits, int wsize = 8) {
+  auto power_of_2_bits = (bits & (bits - 1)) == 0;
+  return power_of_2_bits ? (wsize / 8) : (bits == 5 ? 5 : 3);
+}
+
 template <typename T, int bits>
 void extract_bits(const uint8_t* w_in, T* w_out) {
-  assert(bits == 3 || bits == 6);
+  static_assert(bits == 3 || bits == 5 || bits == 6);
   if (bits == 3) {
     w_out[0] = static_cast<T>(w_in[0] & 0x7);
     w_out[1] = static_cast<T>((w_in[0] & 0x38) >> 3);
@@ -25,6 +34,16 @@ void extract_bits(const uint8_t* w_in, T* w_out) {
     w_out[5] = static_cast<T>(((w_in[1] & 0x80) >> 7) + ((w_in[2] & 0x3) << 1));
     w_out[6] = static_cast<T>((w_in[2] & 0x1c) >> 2);
     w_out[7] = static_cast<T>((w_in[2] & 0xe0) >> 5);
+  } else if (bits == 5) {
+    w_out[0] = static_cast<T>(w_in[0] & 0x1f);
+    w_out[1] = static_cast<T>(((w_in[0] & 0xe0) >> 5) + ((w_in[1] & 0x3) << 3));
+    w_out[2] = static_cast<T>((w_in[1] & 0x7c) >> 2);
+    w_out[3] = static_cast<T>(((w_in[1] & 0x80) >> 7) + ((w_in[2] & 0xf) << 1));
+    w_out[4] = static_cast<T>(((w_in[2] & 0xf0) >> 4) + ((w_in[3] & 0x1) << 4));
+    w_out[5] = static_cast<T>((w_in[3] & 0x3e) >> 1);
+    w_out[6] = static_cast<T>(((w_in[3] & 0xc0) >> 6) + ((w_in[4] & 0x7) << 2));
+    w_out[7] = static_cast<T>((w_in[4] & 0xf8) >> 3);
+
   } else if (bits == 6) {
     w_out[0] = static_cast<T>(w_in[0] & 0x3f);
     w_out[1] =
@@ -46,8 +65,8 @@ void _qmm(
     int N,
     int K) {
   constexpr int bitmask = (1 << bits) - 1;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
-  constexpr int bytes_per_pack = (bits == 3 || bits == 6) ? 3 : 1;
+  constexpr int pack_factor = get_pack_factor(bits, 8);
+  constexpr int bytes_per_pack = get_bytes_per_pack(bits);
   constexpr int packs_in_group = group_size / pack_factor;
 
   for (int m = 0; m < M; m++) {
@@ -65,7 +84,7 @@ void _qmm(
         T scale = *scales_local++;
         T bias = *biases_local++;
         for (int ng = 0; ng < packs_in_group; ng++) {
-          if (bits == 3 || bits == 6) {
+          if constexpr (bits == 3 || bits == 5 || bits == 6) {
             T wl[pack_factor];
             extract_bits<T, bits>(w_local, wl);
 #pragma clang loop unroll(full)
@@ -104,8 +123,9 @@ void _qmm_t(
     int N,
     int K) {
   constexpr int bitmask = (1 << bits) - 1;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
-  constexpr int bytes_per_pack = (bits == 3 || bits == 6) ? 3 : 1;
+
+  constexpr int pack_factor = get_pack_factor(bits, 8);
+  constexpr int bytes_per_pack = get_bytes_per_pack(bits);
   constexpr int packs_in_group = group_size / pack_factor;
 
   for (int m = 0; m < M; m++) {
@@ -121,7 +141,7 @@ void _qmm_t(
         T bias = *biases_local++;
 
         for (int kw = 0; kw < packs_in_group; kw++) {
-          if (bits == 3 || bits == 6) {
+          if constexpr (bits == 3 || bits == 5 || bits == 6) {
             T wl[pack_factor];
             extract_bits<T, bits>(w_local, wl);
 #pragma clang loop unroll(full)
@@ -304,6 +324,10 @@ void _qmm_dispatch_typed(
       _qmm_dispatch_group<T, 4>(
           result, x, w, scales, biases, M, N, K, group_size, transposed_w);
       break;
+    case 5:
+      _qmm_dispatch_group<T, 5>(
+          result, x, w, scales, biases, M, N, K, group_size, transposed_w);
+      break;
     case 6:
       _qmm_dispatch_group<T, 6>(
           result, x, w, scales, biases, M, N, K, group_size, transposed_w);
@@ -613,9 +637,8 @@ void quantize(
   float eps = 1e-7;
 
   bool power_of_2_bits = is_power_of_2(bits);
-  int el_per_int = bits == 3 ? 8 : bits == 6 ? 4 : 32 / bits;
-  // For 3/6 bits we read 3 uint8s at a time instead of 1 uint32
-  int bytes_per_pack = power_of_2_bits ? 1 : 3;
+  int el_per_int = get_pack_factor(bits, 32);
+  int bytes_per_pack = get_bytes_per_pack(bits);
   int int_per_group = group_size * bytes_per_pack / el_per_int;
   size_t n_groups = w_size / group_size;
 
@@ -640,15 +663,21 @@ void quantize(
     }
     size_t out_idx = i * int_per_group;
     for (int j = 0; j < int_per_group / bytes_per_pack; ++j) {
-      uint32_t out_el = 0;
+      uint64_t out_el = 0;
       for (int k = 0; k < el_per_int; ++k) {
         float w_el = w[w_idx + j * el_per_int + k];
         w_el = std::rint((w_el - bias) / scale);
         w_el = std::min(std::max(w_el, 0.0f), n_bins);
-        out_el |= static_cast<uint32_t>(w_el) << (k * bits);
+        out_el |= static_cast<uint64_t>(w_el) << (k * bits);
       }
       if (power_of_2_bits) {
         out[out_idx + j] = out_el;
+      } else if (bits == 5) {
+        out[out_idx + bytes_per_pack * j] = out_el & 0xff;
+        out[out_idx + bytes_per_pack * j + 1] = (out_el & 0xff00) >> 8;
+        out[out_idx + bytes_per_pack * j + 2] = (out_el & 0xff0000) >> 16;
+        out[out_idx + bytes_per_pack * j + 3] = (out_el & 0xff000000) >> 24;
+        out[out_idx + bytes_per_pack * j + 4] = (out_el & 0xff00000000) >> 32;
       } else {
         out[out_idx + bytes_per_pack * j] = out_el & 0xff;
         out[out_idx + bytes_per_pack * j + 1] = (out_el & 0xff00) >> 8;

mlx/backend/metal/kernels/quantized.h

@@ -14,11 +14,23 @@ using namespace metal;
 MLX_MTL_CONST int SIMD_SIZE = 32;
 MLX_MTL_CONST int QUAD_SIZE = 4;
 
+template <int bits, int wsize = 8>
+inline constexpr short get_pack_factor() {
+  return (bits == 3 || bits == 5) ? 8 : (bits == 6 ? 4 : wsize / bits);
+}
+
+template <int bits, int wsize = 8>
+inline constexpr short get_bytes_per_pack() {
+  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
+  return power_of_2_bits ? (wsize / 8) : (bits == 5 ? 5 : 3);
+}
+
 template <typename T, typename U, int values_per_thread, int bits>
 inline U load_vector(const device T* x, thread U* x_thread) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   U sum = 0;
 
@@ -57,6 +69,21 @@ inline U load_vector(const device T* x, thread U* x_thread) {
     }
   }
 
+  else if (bits == 5) {
+    for (int i = 0; i < values_per_thread; i += 8) {
+      sum += x[i] + x[i + 1] + x[i + 2] + x[i + 3] + x[i + 4] + x[i + 5] +
+          x[i + 6] + x[i + 7];
+      x_thread[i] = x[i];
+      x_thread[i + 1] = x[i + 1] / 32.0f;
+      x_thread[i + 2] = x[i + 2] / 4.0f;
+      x_thread[i + 3] = x[i + 3] / 128.0f;
+      x_thread[i + 4] = x[i + 4] / 16.0f;
+      x_thread[i + 5] = x[i + 5] / 2.0f;
+      x_thread[i + 6] = x[i + 6] / 64.0f;
+      x_thread[i + 7] = x[i + 7] / 8.0f;
+    }
+  }
+
   else if (bits == 6) {
     for (int i = 0; i < values_per_thread; i += 4) {
       sum += x[i] + x[i + 1] + x[i + 2] + x[i + 3];
@@ -80,8 +107,9 @@ inline U load_vector(const device T* x, thread U* x_thread) {
 template <typename T, typename U, int values_per_thread, int bits>
 inline U load_vector_safe(const device T* x, thread U* x_thread, int N) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   U sum = 0;
 
@@ -121,6 +149,21 @@ inline U load_vector_safe(const device T* x, thread U* x_thread, int N) {
     }
   }
 
+  else if (bits == 5) {
+    for (int i = 0; i < N; i += 8) {
+      sum += x[i] + x[i + 1] + x[i + 2] + x[i + 3] + x[i + 4] + x[i + 5] +
+          x[i + 6] + x[i + 7];
+      x_thread[i] = x[i];
+      x_thread[i + 1] = x[i + 1] / 32.0f;
+      x_thread[i + 2] = x[i + 2] / 4.0f;
+      x_thread[i + 3] = x[i + 3] / 128.0f;
+      x_thread[i + 4] = x[i + 4] / 16.0f;
+      x_thread[i + 5] = x[i + 5] / 2.0f;
+      x_thread[i + 6] = x[i + 6] / 64.0f;
+      x_thread[i + 7] = x[i + 7] / 8.0f;
+    }
+  }
+
   else if (bits == 6) {
     for (int i = 0; i < N; i += 4) {
       sum += x[i] + x[i + 1] + x[i + 2] + x[i + 3];
@@ -153,8 +196,9 @@ inline U qdot(
     U bias,
     U sum) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   U accum = 0;
 
@@ -199,6 +243,26 @@ inline U qdot(
     }
   }
 
+  else if (bits == 5) {
+    for (int i = 0; i < (values_per_thread / 8); i++) {
+      x_thread += 8 * i;
+      w += 5 * i;
+
+      accum += (w[0] & 0x1f) * x_thread[0];
+      accum += (w[0] & 0xe0) * x_thread[1];
+      accum += (w[1] & 0x3) * (x_thread[1] * 256.0f);
+      accum += (w[1] & 0x7c) * x_thread[2];
+      accum += (w[1] & 0x80) * x_thread[3];
+      accum += (w[2] & 0xf) * (x_thread[3] * 256.0f);
+      accum += (w[2] & 0xf0) * x_thread[4];
+      accum += (w[3] & 0x1) * (x_thread[4] * 256.0f);
+      accum += (w[3] & 0x3e) * x_thread[5];
+      accum += (w[3] & 0xc0) * x_thread[6];
+      accum += (w[4] & 0x7) * (x_thread[6] * 256.0f);
+      accum += (w[4] & 0xf8) * x_thread[7];
+    }
+  }
+
   else if (bits == 6) {
     for (int i = 0; i < (values_per_thread / 4); i++) {
       x_thread += 4 * i;
@@ -234,8 +298,9 @@ inline U qdot_safe(
     U sum,
     int N) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   U accum = 0;
 
@@ -280,6 +345,26 @@ inline U qdot_safe(
     }
   }
 
+  else if (bits == 5) {
+    for (int i = 0; i < (N / 8); i++) {
+      x_thread += 8 * i;
+      w += 5 * i;
+
+      accum += (w[0] & 0x1f) * x_thread[0];
+      accum += (w[0] & 0xe0) * x_thread[1];
+      accum += (w[1] & 0x3) * (x_thread[1] * 256.0f);
+      accum += (w[1] & 0x7c) * x_thread[2];
+      accum += (w[1] & 0x80) * x_thread[3];
+      accum += (w[2] & 0xf) * (x_thread[3] * 256.0f);
+      accum += (w[2] & 0xf0) * x_thread[4];
+      accum += (w[3] & 0x1) * (x_thread[4] * 256.0f);
+      accum += (w[3] & 0x3e) * x_thread[5];
+      accum += (w[3] & 0xc0) * x_thread[6];
+      accum += (w[4] & 0x7) * (x_thread[6] * 256.0f);
+      accum += (w[4] & 0xf8) * x_thread[7];
+    }
+  }
+
   else if (bits == 6) {
     for (int i = 0; i < (N / 4); i++) {
       x_thread += 4 * i;
@@ -310,8 +395,9 @@ template <typename U, int values_per_thread, int bits>
 inline void
 qouter(const thread uint8_t* w, U x, U scale, U bias, thread U* result) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   if (bits == 2) {
     U s[4] = {scale, scale / 4.0f, scale / 16.0f, scale / 64.0f};
@@ -348,8 +434,31 @@ qouter(const thread uint8_t* w, U x, U scale, U bias, thread U* result) {
       result[2 * i] += x * (s[0] * (w[i] & 0x0f) + bias);
       result[2 * i + 1] += x * (s[1] * (w[i] & 0xf0) + bias);
     }
+  }
 
-  } else if (bits == 6) {
+  else if (bits == 5) {
+    for (int i = 0; i < (values_per_thread / 8); i++) {
+      uint8_t w0 = w[5 * i];
+      uint8_t w1 = w[5 * i + 1];
+      uint8_t w2 = w[5 * i + 2];
+      uint8_t w3 = w[5 * i + 3];
+      uint8_t w4 = w[5 * i + 4];
+      result[8 * i] += x * ((w0 & 0x1f) * scale + bias);
+      result[8 * i + 1] +=
+          x * ((((w0 & 0xe0) >> 5) + ((w1 & 0x3) << 3)) * scale + bias);
+      result[8 * i + 2] += x * (((w1 & 0x7c) >> 2) * scale + bias);
+      result[8 * i + 3] +=
+          x * ((((w1 & 0x80) >> 7) + ((w2 & 0xf) << 1)) * scale + bias);
+      result[8 * i + 4] +=
+          x * ((((w2 & 0xf0) >> 4) + ((w3 & 0x1) << 4)) * scale + bias);
+      result[8 * i + 5] += x * (((w3 & 0x3e) >> 1) * scale + bias);
+      result[8 * i + 6] +=
+          x * ((((w3 & 0xc0) >> 6) + ((w4 & 0x7) << 2)) * scale + bias);
+      result[8 * i + 7] += x * (((w4 & 0xf8) >> 3) * scale + bias);
+    }
+  }
+
+  else if (bits == 6) {
     for (int i = 0; i < (values_per_thread / 4); i++) {
       uint8_t w0 = w[3 * i];
       uint8_t w1 = w[3 * i + 1];
@@ -375,8 +484,9 @@ template <typename U, int N, int bits>
 inline void
 dequantize(const device uint8_t* w, U scale, U bias, threadgroup U* w_local) {
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
   if (bits == 2) {
     U s[4] = {
@@ -416,11 +526,26 @@ dequantize(const device uint8_t* w, U scale, U bias, threadgroup U* w_local) {
     }
   }
 
+  else if (bits == 5) {
+    for (int i = 0; i < (N / 8); i++) {
+      w_local += 8 * i;
+      w += 5 * i;
+
+      w_local[0] = (w[0] & 0x1f) * scale + bias;
+      w_local[1] = (((w[0] & 0xe0) >> 5) + ((w[1] & 0x3) << 3)) * scale + bias;
+      w_local[2] = ((w[1] & 0x7c) >> 2) * scale + bias;
+      w_local[3] = (((w[1] & 0x80) >> 7) + ((w[2] & 0xf) << 1)) * scale + bias;
+      w_local[4] = (((w[2] & 0xf0) >> 4) + ((w[3] & 0x1) << 4)) * scale + bias;
+      w_local[5] = ((w[3] & 0x3e) >> 1) * scale + bias;
+      w_local[6] = (((w[3] & 0xc0) >> 6) + ((w[4] & 0x7) << 2)) * scale + bias;
+      w_local[7] = ((w[4] & 0xf8) >> 3) * scale + bias;
+    }
+  }
+
   else if (bits == 6) {
     for (int i = 0; i < (N / 4); i++) {
       w_local += 4 * i;
       w += 3 * i;
-
       w_local[0] = (w[0] & 0x3f) * scale + bias;
       w_local[1] = (((w[0] >> 6) & 0x03) + ((w[1] & 0x0f) << 2)) * scale + bias;
       w_local[2] = (((w[1] >> 4) & 0x0f) + ((w[2] & 0x03) << 4)) * scale + bias;
@@ -452,11 +577,12 @@ struct QuantizedBlockLoader {
       group_size % BCOLS == 0,
       "The group size should be divisible by the columns");
   static_assert(
-      bits == 2 || bits == 3 || bits == 4 || bits == 6 || bits == 8,
-      "Template undefined for bits not in {2, 3, 4, 6, 8}");
+      bits == 2 || bits == 3 || bits == 4 || bits == 5 || bits == 6 ||
+          bits == 8,
+      "Template undefined for bits not in {2, 3, 4, 5, 6, 8}");
 
-  MLX_MTL_CONST short pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
-  MLX_MTL_CONST short bytes_per_pack = (bits == 3 || bits == 6) ? 3 : 1;
+  MLX_MTL_CONST short pack_factor = get_pack_factor<bits, 8>();
+  MLX_MTL_CONST short bytes_per_pack = get_bytes_per_pack<bits>();
   MLX_MTL_CONST short BCOLS_PACKED = BCOLS / pack_factor;
   MLX_MTL_CONST short n_reads =
       (BCOLS_PACKED * BROWS < tgp_size) ? 1 : (BCOLS_PACKED * BROWS) / tgp_size;
@@ -632,12 +758,11 @@ METAL_FUNC void qmv_fast_impl(
     uint3 tid [[threadgroup_position_in_grid]],
     uint simd_gid [[simdgroup_index_in_threadgroup]],
     uint simd_lid [[thread_index_in_simdgroup]]) {
-  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
   constexpr int packs_per_thread = bits == 2 ? 1 : 2;
   constexpr int num_simdgroups = 2;
   constexpr int results_per_simdgroup = 4;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 32 / bits;
-  constexpr int bytes_per_pack = power_of_2_bits ? 4 : 3;
+  constexpr int pack_factor = get_pack_factor<bits, 32>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits, 32>();
   constexpr int values_per_thread = pack_factor * packs_per_thread;
   constexpr int block_size = values_per_thread * SIMD_SIZE;
   constexpr int scale_step_per_thread = group_size / values_per_thread;
@@ -700,12 +825,12 @@ METAL_FUNC void qmv_impl(
     uint3 tid [[threadgroup_position_in_grid]],
     uint simd_gid [[simdgroup_index_in_threadgroup]],
     uint simd_lid [[thread_index_in_simdgroup]]) {
-  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
   constexpr int num_simdgroups = 2;
   constexpr int results_per_simdgroup = 4;
   constexpr int packs_per_thread = 1;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 32 / bits;
-  constexpr int bytes_per_pack = power_of_2_bits ? 4 : 3;
+  constexpr int pack_factor = get_pack_factor<bits, 32>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits, 32>();
+
   constexpr int values_per_thread = pack_factor * packs_per_thread;
   constexpr int block_size = values_per_thread * SIMD_SIZE;
   constexpr int scale_step_per_thread = group_size / values_per_thread;
@@ -857,8 +982,9 @@ METAL_FUNC void qvm_impl(
     uint simd_lid [[thread_index_in_simdgroup]]) {
   constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
   constexpr int num_simdgroups = 2;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 32 / bits;
-  constexpr int bytes_per_pack = power_of_2_bits ? 1 : 3;
+  constexpr int pack_factor = get_pack_factor<bits, 32>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
+
   constexpr int tn = 32 / pack_factor;
   constexpr int block_size = SIMD_SIZE;
 
@@ -981,9 +1107,10 @@ METAL_FUNC void qmm_t_impl(
 
   constexpr int WM = 2;
   constexpr int WN = 2;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
+  constexpr int pack_factor = get_pack_factor<bits, 8>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
+
   constexpr int BK_padded = (BK + 16 / sizeof(T));
-  constexpr int bytes_per_pack = (bits == 3 || bits == 6) ? 3 : 1;
 
   // Instantiate the appropriate BlockMMA and Loader
   using mma_t = mlx::steel::
@@ -1106,11 +1233,11 @@ METAL_FUNC void qmm_n_impl(
 
   constexpr int WM = 2;
   constexpr int WN = 2;
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
+  constexpr int pack_factor = get_pack_factor<bits, 8>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
+
   constexpr int BK_padded = (BK + 16 / sizeof(T));
   constexpr int BN_padded = (BN + 16 / sizeof(T));
-  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
-  constexpr int bytes_per_pack = power_of_2_bits ? 1 : 3;
 
   // Instantiate the appropriate BlockMMA and Loader
   using mma_t = mlx::steel::
@@ -2120,11 +2247,10 @@ template <
     uint3 tid [[threadgroup_position_in_grid]],
     uint simd_group_id [[simdgroup_index_in_threadgroup]],
     uint simd_lane_id [[thread_index_in_simdgroup]]) {
-  constexpr int pack_factor = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
+  constexpr int pack_factor = get_pack_factor<bits, 8>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
   constexpr int BK_padded = (BK + 16 / sizeof(T));
   constexpr int BN_padded = (BN + 16 / sizeof(T));
-  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
-  constexpr int bytes_per_pack = power_of_2_bits ? 1 : 3;
 
   using mma_t = mlx::steel::BlockMMA<
       T,
@@ -2305,13 +2431,13 @@ template <typename T, const int group_size, const int bits>
   constexpr float eps = 1e-7;
   constexpr int simd_size = 32;
   constexpr float n_bins = (1 << bits) - 1;
-  constexpr int packs_per_int = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
+  constexpr int pack_factor = get_pack_factor<bits, 8>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
   constexpr int values_per_reduce = group_size / simd_size;
-  constexpr int writes_per_reduce = packs_per_int / values_per_reduce;
+  constexpr int writes_per_reduce = pack_factor / values_per_reduce;
   constexpr int writes_per_pack =
-      writes_per_reduce > 1 ? 1 : values_per_reduce / packs_per_int;
+      writes_per_reduce > 1 ? 1 : values_per_reduce / pack_factor;
   constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
-  constexpr int bytes_per_pack = power_of_2_bits ? 1 : 3;
 
   static_assert(
       group_size % simd_size == 0,
@@ -2354,8 +2480,8 @@ template <typename T, const int group_size, const int bits>
     biases[gindex] = static_cast<T>(bias);
   }
 
-  // We accumulate 3 bytes worth for 3/6 bit so we need a uint32_t
-  uint32_t output = 0;
+  using OutType = metal::conditional_t<bits == 5, uint64_t, uint32_t>;
+  OutType output = 0;
 
 #pragma clang loop unroll(full)
   for (int i = 0; i < values_per_reduce; i++) {
@@ -2363,27 +2489,35 @@ template <typename T, const int group_size, const int bits>
     if (bits == 8) {
       output = val;
     } else {
-      output += val << (bits * (i % packs_per_int));
+      output |= val << (bits * (i % pack_factor));
     }
 
-    if (packs_per_int < values_per_reduce &&
-        i % packs_per_int == packs_per_int - 1) {
-      out[out_index + i / packs_per_int] = output;
+    if (pack_factor < values_per_reduce && i % pack_factor == pack_factor - 1) {
+      out[out_index + i / pack_factor] = output;
       output = 0;
     } else {
 #pragma clang loop unroll(full)
       for (int j = 1; j < writes_per_reduce; j++) {
         uint8_t sval = simd_shuffle_down(val, j);
-        output += sval << (bits * (j * values_per_reduce + i));
+        output |= static_cast<OutType>(sval)
+            << (bits * (j * values_per_reduce + i));
       }
     }
   }
   if (bits == 3 || bits == 6) {
-    if (in_index % packs_per_int == 0 && out_index % bytes_per_pack == 0) {
+    if (in_index % pack_factor == 0 && out_index % bytes_per_pack == 0) {
       out[out_index] = output & 0xff;
       out[out_index + 1] = (output & 0xff00) >> 8;
       out[out_index + 2] = (output & 0xff0000) >> 16;
     }
+  } else if (bits == 5) {
+    if (in_index % pack_factor == 0 && out_index % bytes_per_pack == 0) {
+      out[out_index] = output & 0xff;
+      out[out_index + 1] = (output & 0xff00) >> 8;
+      out[out_index + 2] = (output & 0xff0000) >> 16;
+      out[out_index + 3] = (output & 0xff000000) >> 24;
+      out[out_index + 4] = (output & 0xff00000000) >> 32;
+    }
   } else {
     if (writes_per_reduce > 0 && out_index % writes_per_reduce == 0) {
       out[out_index / writes_per_reduce] = output;
@@ -2399,12 +2533,11 @@ template <typename T, const int group_size, const int bits>
     device T* out [[buffer(3)]],
     uint2 index [[thread_position_in_grid]],
     uint2 grid_dim [[threads_per_grid]]) {
-  constexpr int packs_per_int = bits == 3 ? 8 : bits == 6 ? 4 : 8 / bits;
-  constexpr int power_of_2_bits = (bits & (bits - 1)) == 0;
-  constexpr int bytes_per_pack = power_of_2_bits ? 1 : 3;
+  constexpr int pack_factor = get_pack_factor<bits, 8>();
+  constexpr int bytes_per_pack = get_bytes_per_pack<bits>();
 
   size_t offset = index.x + grid_dim.x * size_t(index.y);
-  size_t oindex = offset * packs_per_int;
+  size_t oindex = offset * pack_factor;
   size_t gindex = oindex / group_size;
   T scale = scales[gindex];
   T bias = biases[gindex];
@@ -2421,7 +2554,16 @@ template <typename T, const int group_size, const int bits>
     out[5] = (((w[1] & 0x80) >> 7) + ((w[2] & 0x3) << 1)) * scale + bias;
     out[6] = ((w[2] & 0x1c) >> 2) * scale + bias;
     out[7] = ((w[2] & 0xe0) >> 5) * scale + bias;
-
+  } else if (bits == 5) {
+    w += offset * bytes_per_pack;
+    out[0] = (w[0] & 0x1f) * scale + bias;
+    out[1] = (((w[0] & 0xe0) >> 5) + ((w[1] & 0x3) << 3)) * scale + bias;
+    out[2] = ((w[1] & 0x7c) >> 2) * scale + bias;
+    out[3] = (((w[1] & 0x80) >> 7) + ((w[2] & 0xf) << 1)) * scale + bias;
+    out[4] = (((w[2] & 0xf0) >> 4) + ((w[3] & 0x1) << 4)) * scale + bias;
+    out[5] = ((w[3] & 0x3e) >> 1) * scale + bias;
+    out[6] = (((w[3] & 0xc0) >> 6) + ((w[4] & 0x7) << 2)) * scale + bias;
+    out[7] = ((w[4] & 0xf8) >> 3) * scale + bias;
   } else if (bits == 6) {
     w += offset * bytes_per_pack;
     out[0] = (w[0] & 0x3f) * scale + bias;
@@ -2431,7 +2573,7 @@ template <typename T, const int group_size, const int bits>
   } else {
     uint val = w[offset];
 #pragma clang loop unroll(full)
-    for (int i = 0; i < packs_per_int; i++) {
+    for (int i = 0; i < pack_factor; i++) {
       uint8_t d;
       if (bits == 2) {
         d = (val >> (bits * i)) & 0x03;

mlx/backend/metal/kernels/quantized.metal

@@ -136,6 +136,7 @@
   instantiate_quantized_groups(2) \
   instantiate_quantized_groups(3) \
   instantiate_quantized_groups(4) \
+  instantiate_quantized_groups(5) \
   instantiate_quantized_groups(6) \
   instantiate_quantized_groups(8)
 

mlx/backend/metal/quantized.cpp

@@ -976,7 +976,9 @@ void fast::AffineQuantize::eval_gpu(
   // Treat uint32 as uint8 in kernel
   constexpr int uint8_per_uint32 = 4;
   constexpr int simd_size = 32;
-  int packs_per_int = bits_ == 3 ? 8 : bits_ == 6 ? 4 : 8 / bits_;
+  int packs_per_int = (bits_ == 3 || bits_ == 5) ? 8
+      : bits_ == 6                               ? 4
+                                                 : 8 / bits_;
   int per_thread = dequantize_ ? packs_per_int : group_size_ / simd_size;
   size_t nthreads =
       dequantize_ ? out.size() / packs_per_int : w.size() / per_thread;

mlx/fast.cpp

@@ -839,14 +839,14 @@ affine_quantize(const array& w, int group_size, int bits, StreamOrDevice s_) {
   if (group_size != 32 && group_size != 64 && group_size != 128) {
     std::ostringstream msg;
     msg << "[quantize] The requested group size " << group_size
-        << " is not supported. The supported group sizes are 64 and 128.";
+        << " is not supported. The supported group sizes are 32, 64, and 128.";
     throw std::invalid_argument(msg.str());
   }
 
-  if (bits != 2 && bits != 3 && bits != 4 && bits != 6 && bits != 8) {
+  if (bits < 2 || bits > 8 || bits == 7) {
     std::ostringstream msg;
     msg << "[quantize] The requested number of bits " << bits
-        << " is not supported. The supported bits are 2, 3, 4, 6 and 8.";
+        << " is not supported. The supported bits are 2, 3, 4, 5, 6 and 8.";
     throw std::invalid_argument(msg.str());
   }