llama : support negative ith in llama_get_ API (#6519)

* llama_sampling_sample with default args is more naively usable

* Batches populated by either llama_batch_get_one or llama_batch_add work with default args
  * Previously get_one could use the default argument
  * Previously add should usually have used the last index where logits[idx] == true
* This hopefully encourages the use of llama_batch_add
  * By giving expected results when using default arguments.
* Adds "negative indexing" feature to llama_get_logits_ith and llama_get_embeddings_ith
* Believed to work with any currently well behaved program
  * Default arg now works for both cases (previously would give strange results for add case)
  * Any non-negative number is unaffected and behaves as previously
  * Negative arguments were previously invalid.
* Implemented as a special case of indexing as suggested by @compilade in ggerganov/llama.cpp#6519

* Fixed mismatch type errors

* cited in macOS CI tests
* Missed in original updates based on PR feedback in ggerganov/llama.cpp#6519

common/sampling.h

@@ -129,7 +129,7 @@ llama_token llama_sampling_sample(
  struct llama_sampling_context * ctx_sampling,
  struct llama_context * ctx_main,
  struct llama_context * ctx_cfg,
- int idx = 0);
+ int idx = -1);
 
 // Prepares and adjusts the set of token candidates for sampling based on penalties, biases, and sampling parameters.
 llama_token_data_array llama_sampling_prepare(

llama.cpp

@@ -2179,7 +2179,7 @@ struct llama_context {
 
  std::vector<int32_t> output_ids; // map batch token positions to ids of the logits and embd buffers
  size_t output_size = 0; // capacity (of tokens positions) for the output buffers
- int32_t n_outputs = 0; // number of actually-used outputs in the current ubatch
+ int32_t n_outputs = 0; // number of actually-used outputs in the current ubatch or last logical batch
 
  bool logits_all = false;
 
@@ -10413,6 +10413,9 @@ static int llama_decode_internal(
  n_outputs_prev += lctx.n_outputs;
  }
 
+ // set to total number of outputs in the batch, for use in llama_get_logits_ith
+ lctx.n_outputs = n_outputs;
+
  // wait for the computation to finish (automatically done when obtaining the model output)
  //llama_synchronize(&lctx);
 
@@ -15947,23 +15950,31 @@ float * llama_get_logits(struct llama_context * ctx) {
 }
 
 float * llama_get_logits_ith(struct llama_context * ctx, int32_t i) {
+ int32_t j = -1;
  llama_synchronize(ctx);
 
  try {
  if (ctx->logits == nullptr) {
  throw std::runtime_error("no logits");
  }
- if ((size_t) i >= ctx->output_ids.size()) {
+
+ if (i < 0) {
+ j = ctx->n_outputs + i;
+ if (j < 0) {
+ throw std::runtime_error(format("negative index out of range [0, %d)", ctx->n_outputs));
+ }
+ } else if ((size_t) i >= ctx->output_ids.size()) {
  throw std::runtime_error(format("out of range [0, %lu)", ctx->output_ids.size()));
+ } else {
+ j = ctx->output_ids[i];
  }
- const int32_t j = ctx->output_ids[i];
 
  if (j < 0) {
  throw std::runtime_error(format("batch.logits[%d] != true", i));
  }
- if ((size_t) j >= ctx->output_size) {
+ if (j >= ctx->n_outputs) {
  // This should not happen
- throw std::runtime_error(format("corrupt output buffer (j=%d, output_size=%lu)", j, ctx->output_size));
+ throw std::runtime_error(format("corrupt output buffer (j=%d, n_outputs=%d)", j, ctx->n_outputs));
  }
 
  return ctx->logits + j*ctx->model.hparams.n_vocab;
@@ -15983,23 +15994,32 @@ float * llama_get_embeddings(struct llama_context * ctx) {
 }
 
 float * llama_get_embeddings_ith(struct llama_context * ctx, int32_t i) {
+ int32_t j = -1;
+
  llama_synchronize(ctx);
 
  try {
  if (ctx->embd == nullptr) {
  throw std::runtime_error("no embeddings");
  }
- if ((size_t) i >= ctx->output_ids.size()) {
+
+ if (i < 0) {
+ j = ctx->n_outputs + i;
+ if (j < 0) {
+ throw std::runtime_error(format("negative index out of range [0, %d)", ctx->n_outputs));
+ }
+ } else if ((size_t) i >= ctx->output_ids.size()) {
  throw std::runtime_error(format("out of range [0, %lu)", ctx->output_ids.size()));
+ } else {
+ j = ctx->output_ids[i];
  }
- const int32_t j = ctx->output_ids[i];
 
  if (j < 0) {
  throw std::runtime_error(format("batch.logits[%d] != true", i));
  }
- if ((size_t) j >= ctx->output_size) {
+ if (j >= ctx->n_outputs) {
  // This should not happen
- throw std::runtime_error(format("corrupt output buffer (j=%d, output_size=%lu)", j, ctx->output_size));
+ throw std::runtime_error(format("corrupt output buffer (j=%d, n_outputs=%d)", j, ctx->n_outputs));
  }
 
  return ctx->embd + j*ctx->model.hparams.n_embd;

llama.h

@@ -747,8 +747,9 @@ extern "C" {
  // Cols: n_vocab
  LLAMA_API float * llama_get_logits(struct llama_context * ctx);
 
- // Logits for the ith token. Equivalent to:
+ // Logits for the ith token. For positive indices, Equivalent to:
  // llama_get_logits(ctx) + ctx->output_ids[i]*n_vocab
+ // Negative indicies can be used to access logits in reverse order, -1 is the last logit.
  // returns NULL for invalid ids.
  LLAMA_API float * llama_get_logits_ith(struct llama_context * ctx, int32_t i);
 
@@ -760,8 +761,9 @@ extern "C" {
  // Otherwise, returns NULL.
  LLAMA_API float * llama_get_embeddings(struct llama_context * ctx);
 
- // Get the embeddings for the ith token. Equivalent to:
+ // Get the embeddings for the ith token. For positive indices, Equivalent to:
  // llama_get_embeddings(ctx) + ctx->output_ids[i]*n_embd
+ // Negative indicies can be used to access embeddings in reverse order, -1 is the last embedding.
  // shape: [n_embd] (1-dimensional)
  // returns NULL for invalid ids.
  LLAMA_API float * llama_get_embeddings_ith(struct llama_context * ctx, int32_t i);