From b333b06772c89d96aacb5490d6a219fba7c09cc6 Mon Sep 17 00:00:00 2001
From: Mitja Felicijan <mitja.felicijan@gmail.com>
Date: Thu, 12 Feb 2026 20:57:17 +0100
Subject: Engage!

---
 .../ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl  | 66 ++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 llama.cpp/ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl

(limited to 'llama.cpp/ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl')

diff --git a/llama.cpp/ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl b/llama.cpp/ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl
new file mode 100644
index 0000000..e622552
--- /dev/null
+++ b/llama.cpp/ggml/src/ggml-webgpu/wgsl-shaders/cumsum.wgsl
@@ -0,0 +1,66 @@
+@group(0) @binding(0)
+var<storage, read_write> src: array<f32>;
+
+@group(0) @binding(1)
+var<storage, read_write> dst: array<f32>;
+
+struct Params {
+    offset_src: u32, // in elements
+    offset_dst: u32, // in elements
+    ne0: u32,
+};
+
+@group(0) @binding(2)
+var<uniform> params: Params;
+
+var<workgroup> shared_sum: array<f32, WG_SIZE>;
+
+@compute @workgroup_size(WG_SIZE)
+fn main(@builtin(workgroup_id) wid: vec3<u32>,
+        @builtin(local_invocation_id) lid: vec3<u32>) {
+    let row_idx = params.offset_src + wid.x * params.ne0;
+    let elems = (params.ne0 + WG_SIZE - 1) / WG_SIZE;
+    var local_sum: f32 = 0.0;
+    for (var col = lid.x * elems; col < (lid.x + 1) * elems && col < params.ne0; col ++) {
+        local_sum += src[row_idx + col];
+    }
+    shared_sum[lid.x] = local_sum;
+    workgroupBarrier();
+
+    // upsweep
+    var offset = 1u;
+    while (offset < WG_SIZE) {
+        let idx = (lid.x + 1) * offset * 2 - 1;
+        if (idx < WG_SIZE) {
+            shared_sum[idx] = shared_sum[idx] + shared_sum[idx - offset];
+        }
+        workgroupBarrier();
+        offset <<= 1;
+    }
+
+    // set last to 0 for exclusive sum
+    if (lid.x == 0) {
+        shared_sum[WG_SIZE - 1] = 0.0;
+    }
+    workgroupBarrier();
+
+    // downsweep
+    offset = WG_SIZE >> 1;
+    while (offset > 0) {
+        let idx = (lid.x + 1) * offset * 2 - 1;
+        if (idx < WG_SIZE) {
+            let t = shared_sum[idx - offset];
+            shared_sum[idx - offset] = shared_sum[idx];
+            shared_sum[idx] = shared_sum[idx] + t;
+        }
+        workgroupBarrier();
+        offset = offset >> 1;
+    }
+
+    // shared_sum[lid] is exclusive prefix sum up to this thread.
+    var running_sum = shared_sum[lid.x];
+    for (var col = lid.x * elems; col < (lid.x + 1) * elems && col < params.ne0; col ++) {
+        running_sum += src[row_idx + col];
+        dst[params.offset_dst + wid.x * params.ne0 + col] = running_sum;
+    }
+}
-- 
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