feat: add exponential scheduler (#346)

* feat: added exponential scheduler

* updated README

* improved exponential formatting

---------

Co-authored-by: leejet <leejet714@gmail.com>

README.md

@@ -223,7 +223,7 @@ arguments:
   --rng {std_default, cuda}          RNG (default: cuda)
   -s SEED, --seed SEED               RNG seed (default: 42, use random seed for < 0)
   -b, --batch-count COUNT            number of images to generate.
-  --schedule {discrete, karras, ays, gits} Denoiser sigma schedule (default: discrete)
+  --schedule {discrete, karras, exponential, ays, gits} Denoiser sigma schedule (default: discrete)
   --clip-skip N                      ignore last layers of CLIP network; 1 ignores none, 2 ignores one layer (default: -1)
                                      <= 0 represents unspecified, will be 1 for SD1.x, 2 for SD2.x
   --vae-tiling                       process vae in tiles to reduce memory usage

denoiser.hpp

@@ -42,6 +42,27 @@ struct DiscreteSchedule : SigmaSchedule {
     }
 };
 
+struct ExponentialSchedule : SigmaSchedule {
+    std::vector<float> get_sigmas(uint32_t n, float sigma_min, float sigma_max, t_to_sigma_t t_to_sigma) {
+        std::vector<float> sigmas;
+
+        // Calculate step size
+        float log_sigma_min = std::log(sigma_min);
+        float log_sigma_max = std::log(sigma_max);
+        float step = (log_sigma_max - log_sigma_min) / (n - 1);
+
+        // Fill sigmas with exponential values
+        for (uint32_t i = 0; i < n; ++i) {
+            float sigma = std::exp(log_sigma_max - step * i);
+            sigmas.push_back(sigma);
+        }
+
+        sigmas.push_back(0.0f);
+
+        return sigmas;
+    }
+};
+
 /* interp and linear_interp adapted from dpilger26's NumCpp library:
  * https://github.com/dpilger26/NumCpp/tree/5e40aab74d14e257d65d3dc385c9ff9e2120c60e */
 constexpr double interp(double left, double right, double perc) noexcept {

examples/cli/main.cpp

@@ -46,6 +46,7 @@ const char* schedule_str[] = {
     "default",
     "discrete",
     "karras",
+    "exponential",
     "ays",
     "gits",
 };
@@ -203,7 +204,7 @@ void print_usage(int argc, const char* argv[]) {
     printf("  --rng {std_default, cuda}          RNG (default: cuda)\n");
     printf("  -s SEED, --seed SEED               RNG seed (default: 42, use random seed for < 0)\n");
     printf("  -b, --batch-count COUNT            number of images to generate.\n");
-    printf("  --schedule {discrete, karras, ays, gits} Denoiser sigma schedule (default: discrete)\n");
+    printf("  --schedule {discrete, karras, exponential, ays, gits} Denoiser sigma schedule (default: discrete)\n");
     printf("  --clip-skip N                      ignore last layers of CLIP network; 1 ignores none, 2 ignores one layer (default: -1)\n");
     printf("                                     <= 0 represents unspecified, will be 1 for SD1.x, 2 for SD2.x\n");
     printf("  --vae-tiling                       process vae in tiles to reduce memory usage\n");

stable-diffusion.cpp

@@ -538,6 +538,10 @@ public:
                     LOG_INFO("running with Karras schedule");
                     denoiser->schedule = std::make_shared<KarrasSchedule>();
                     break;
+                case EXPONENTIAL:
+                    LOG_INFO("running exponential schedule");
+                    denoiser->schedule = std::make_shared<ExponentialSchedule>();
+                    break;
                 case AYS:
                     LOG_INFO("Running with Align-Your-Steps schedule");
                     denoiser->schedule          = std::make_shared<AYSSchedule>();

stable-diffusion.h

@@ -51,6 +51,7 @@ enum schedule_t {
     DEFAULT,
     DISCRETE,
     KARRAS,
+    EXPONENTIAL,
     AYS,
     GITS,
     N_SCHEDULES