Use hash based filtering instead of stochastic

gpuweb · Mar 6, 2024 · c8800ee · c8800ee
1 parent c362232
commit c8800ee
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Showing 9 changed files with 179 additions and 198 deletions.
diff --git a/src/resources/cache/hashes.json b/src/resources/cache/hashes.json
@@ -1,110 +1,110 @@
 {
-  "webgpu/shader/execution/binary/af_addition.bin": "3537bbf",
-  "webgpu/shader/execution/binary/af_logical.bin": "a483b968",
-  "webgpu/shader/execution/binary/af_division.bin": "8759f887",
-  "webgpu/shader/execution/binary/af_matrix_addition.bin": "3eb7b746",
-  "webgpu/shader/execution/binary/af_matrix_subtraction.bin": "a1173db6",
-  "webgpu/shader/execution/binary/af_multiplication.bin": "b77f680a",
-  "webgpu/shader/execution/binary/af_remainder.bin": "c4697dfb",
-  "webgpu/shader/execution/binary/af_subtraction.bin": "17624e58",
-  "webgpu/shader/execution/binary/f16_addition.bin": "32b920a0",
-  "webgpu/shader/execution/binary/f16_logical.bin": "b89ca9b9",
-  "webgpu/shader/execution/binary/f16_division.bin": "e1e74564",
-  "webgpu/shader/execution/binary/f16_matrix_addition.bin": "37418ae2",
-  "webgpu/shader/execution/binary/f16_matrix_matrix_multiplication.bin": "f9e16ada",
-  "webgpu/shader/execution/binary/f16_matrix_scalar_multiplication.bin": "739ecb65",
-  "webgpu/shader/execution/binary/f16_matrix_subtraction.bin": "c20eaf83",
-  "webgpu/shader/execution/binary/f16_matrix_vector_multiplication.bin": "1e0127c0",
-  "webgpu/shader/execution/binary/f16_multiplication.bin": "e89c81f8",
-  "webgpu/shader/execution/binary/f16_remainder.bin": "85339fca",
-  "webgpu/shader/execution/binary/f16_subtraction.bin": "cd4bf3d3",
-  "webgpu/shader/execution/binary/f32_addition.bin": "9eaa0e04",
-  "webgpu/shader/execution/binary/f32_logical.bin": "c7370c09",
-  "webgpu/shader/execution/binary/f32_division.bin": "a81fa2e1",
-  "webgpu/shader/execution/binary/f32_matrix_addition.bin": "e3a3f2a2",
-  "webgpu/shader/execution/binary/f32_matrix_matrix_multiplication.bin": "51146714",
-  "webgpu/shader/execution/binary/f32_matrix_scalar_multiplication.bin": "99d99f13",
-  "webgpu/shader/execution/binary/f32_matrix_subtraction.bin": "dfab64d5",
-  "webgpu/shader/execution/binary/f32_matrix_vector_multiplication.bin": "f7de887d",
-  "webgpu/shader/execution/binary/f32_multiplication.bin": "ec380a2f",
-  "webgpu/shader/execution/binary/f32_remainder.bin": "8113a345",
-  "webgpu/shader/execution/binary/f32_subtraction.bin": "c65c7882",
-  "webgpu/shader/execution/binary/i32_arithmetic.bin": "a0b0a016",
-  "webgpu/shader/execution/binary/i32_comparison.bin": "f3d9b3f9",
-  "webgpu/shader/execution/binary/u32_arithmetic.bin": "16e32fd",
-  "webgpu/shader/execution/binary/u32_comparison.bin": "da33cc5d",
-  "webgpu/shader/execution/abs.bin": "e7d0db43",
-  "webgpu/shader/execution/acos.bin": "5c26b875",
-  "webgpu/shader/execution/acosh.bin": "6006745a",
-  "webgpu/shader/execution/asin.bin": "bd0a6605",
-  "webgpu/shader/execution/asinh.bin": "871eabc6",
-  "webgpu/shader/execution/atan.bin": "87e5508e",
-  "webgpu/shader/execution/atan2.bin": "587e430f",
-  "webgpu/shader/execution/atanh.bin": "24973287",
-  "webgpu/shader/execution/bitcast.bin": "d3767f75",
-  "webgpu/shader/execution/ceil.bin": "3597359f",
-  "webgpu/shader/execution/clamp.bin": "db80e3d4",
-  "webgpu/shader/execution/cos.bin": "be6a43df",
-  "webgpu/shader/execution/cosh.bin": "6b1522b4",
-  "webgpu/shader/execution/cross.bin": "6e12c696",
-  "webgpu/shader/execution/degrees.bin": "272d85f9",
-  "webgpu/shader/execution/determinant.bin": "e8c0910f",
-  "webgpu/shader/execution/distance.bin": "fcd1a459",
-  "webgpu/shader/execution/dot.bin": "6cb8305e",
-  "webgpu/shader/execution/exp.bin": "340a4471",
-  "webgpu/shader/execution/exp2.bin": "c3483a4f",
-  "webgpu/shader/execution/faceForward.bin": "2d7047cb",
-  "webgpu/shader/execution/floor.bin": "64eb44f3",
-  "webgpu/shader/execution/fma.bin": "af8fc9a1",
-  "webgpu/shader/execution/fract.bin": "546bfc4b",
-  "webgpu/shader/execution/frexp.bin": "73131e48",
-  "webgpu/shader/execution/inverseSqrt.bin": "af8b8480",
-  "webgpu/shader/execution/ldexp.bin": "b5d05356",
-  "webgpu/shader/execution/length.bin": "87a7a79e",
-  "webgpu/shader/execution/log.bin": "d7929d6d",
-  "webgpu/shader/execution/log2.bin": "4ba66d33",
-  "webgpu/shader/execution/max.bin": "ebc85f1f",
-  "webgpu/shader/execution/min.bin": "5b60cb58",
-  "webgpu/shader/execution/mix.bin": "c8ec2505",
-  "webgpu/shader/execution/modf.bin": "de35d27c",
-  "webgpu/shader/execution/normalize.bin": "1824edd9",
-  "webgpu/shader/execution/pack2x16float.bin": "e6859c1a",
-  "webgpu/shader/execution/pow.bin": "6b8532ae",
-  "webgpu/shader/execution/quantizeToF16.bin": "4956513f",
-  "webgpu/shader/execution/radians.bin": "199010e",
-  "webgpu/shader/execution/reflect.bin": "995fae9e",
-  "webgpu/shader/execution/refract.bin": "181fbbc8",
-  "webgpu/shader/execution/round.bin": "98dce70b",
-  "webgpu/shader/execution/saturate.bin": "3060e843",
-  "webgpu/shader/execution/sign.bin": "7879f29c",
-  "webgpu/shader/execution/sin.bin": "1f3d20e3",
-  "webgpu/shader/execution/sinh.bin": "749425d6",
-  "webgpu/shader/execution/smoothstep.bin": "3b82bce3",
-  "webgpu/shader/execution/sqrt.bin": "b2e5210a",
-  "webgpu/shader/execution/step.bin": "7d27ada6",
-  "webgpu/shader/execution/tan.bin": "a9edf243",
-  "webgpu/shader/execution/tanh.bin": "a733eb02",
-  "webgpu/shader/execution/transpose.bin": "f1a8852b",
-  "webgpu/shader/execution/trunc.bin": "3a3cf31f",
-  "webgpu/shader/execution/unpack2x16float.bin": "e3450db3",
-  "webgpu/shader/execution/unpack2x16snorm.bin": "beb21243",
-  "webgpu/shader/execution/unpack2x16unorm.bin": "37aab928",
-  "webgpu/shader/execution/unpack4x8snorm.bin": "1b57ee27",
-  "webgpu/shader/execution/unpack4x8unorm.bin": "19b3ac32",
-  "webgpu/shader/execution/unary/af_arithmetic.bin": "113dbf1a",
-  "webgpu/shader/execution/unary/af_assignment.bin": "47945f59",
+  "webgpu/shader/execution/binary/af_addition.bin": "ef1b2a5a",
+  "webgpu/shader/execution/binary/af_logical.bin": "2f3b0449",
+  "webgpu/shader/execution/binary/af_division.bin": "91f6a50e",
+  "webgpu/shader/execution/binary/af_matrix_addition.bin": "68f06b6d",
+  "webgpu/shader/execution/binary/af_matrix_subtraction.bin": "a29b1b2a",
+  "webgpu/shader/execution/binary/af_multiplication.bin": "5b249b97",
+  "webgpu/shader/execution/binary/af_remainder.bin": "c746b1c6",
+  "webgpu/shader/execution/binary/af_subtraction.bin": "c4f02864",
+  "webgpu/shader/execution/binary/f16_addition.bin": "deaa570d",
+  "webgpu/shader/execution/binary/f16_logical.bin": "bdeecd90",
+  "webgpu/shader/execution/binary/f16_division.bin": "ad886bb9",
+  "webgpu/shader/execution/binary/f16_matrix_addition.bin": "e3e830b4",
+  "webgpu/shader/execution/binary/f16_matrix_matrix_multiplication.bin": "1efcd108",
+  "webgpu/shader/execution/binary/f16_matrix_scalar_multiplication.bin": "6e681e70",
+  "webgpu/shader/execution/binary/f16_matrix_subtraction.bin": "e1be7c7f",
+  "webgpu/shader/execution/binary/f16_matrix_vector_multiplication.bin": "fbf28fa0",
+  "webgpu/shader/execution/binary/f16_multiplication.bin": "89d45ebd",
+  "webgpu/shader/execution/binary/f16_remainder.bin": "d31a6d89",
+  "webgpu/shader/execution/binary/f16_subtraction.bin": "bce603a2",
+  "webgpu/shader/execution/binary/f32_addition.bin": "316d2809",
+  "webgpu/shader/execution/binary/f32_logical.bin": "ef594391",
+  "webgpu/shader/execution/binary/f32_division.bin": "b687682c",
+  "webgpu/shader/execution/binary/f32_matrix_addition.bin": "6618fb53",
+  "webgpu/shader/execution/binary/f32_matrix_matrix_multiplication.bin": "43239b66",
+  "webgpu/shader/execution/binary/f32_matrix_scalar_multiplication.bin": "9ae2bcf8",
+  "webgpu/shader/execution/binary/f32_matrix_subtraction.bin": "9725b06c",
+  "webgpu/shader/execution/binary/f32_matrix_vector_multiplication.bin": "b3bd584e",
+  "webgpu/shader/execution/binary/f32_multiplication.bin": "801d9d66",
+  "webgpu/shader/execution/binary/f32_remainder.bin": "ece8752c",
+  "webgpu/shader/execution/binary/f32_subtraction.bin": "bd1f20dd",
+  "webgpu/shader/execution/binary/i32_arithmetic.bin": "a8e31d1d",
+  "webgpu/shader/execution/binary/i32_comparison.bin": "cb513412",
+  "webgpu/shader/execution/binary/u32_arithmetic.bin": "3a4e8b28",
+  "webgpu/shader/execution/binary/u32_comparison.bin": "f4faed06",
+  "webgpu/shader/execution/abs.bin": "c56243f5",
+  "webgpu/shader/execution/acos.bin": "d671944f",
+  "webgpu/shader/execution/acosh.bin": "aef9992d",
+  "webgpu/shader/execution/asin.bin": "a3c6f5df",
+  "webgpu/shader/execution/asinh.bin": "be442250",
+  "webgpu/shader/execution/atan.bin": "deefe71",
+  "webgpu/shader/execution/atan2.bin": "81217b83",
+  "webgpu/shader/execution/atanh.bin": "6843748a",
+  "webgpu/shader/execution/bitcast.bin": "344cc17a",
+  "webgpu/shader/execution/ceil.bin": "a4d239a0",
+  "webgpu/shader/execution/clamp.bin": "1e63217d",
+  "webgpu/shader/execution/cos.bin": "e6c1fdc4",
+  "webgpu/shader/execution/cosh.bin": "cdd1f595",
+  "webgpu/shader/execution/cross.bin": "adb0bbf5",
+  "webgpu/shader/execution/degrees.bin": "b594d698",
+  "webgpu/shader/execution/determinant.bin": "73407c59",
+  "webgpu/shader/execution/distance.bin": "2e1c9ab4",
+  "webgpu/shader/execution/dot.bin": "1028309a",
+  "webgpu/shader/execution/exp.bin": "1bc92f9a",
+  "webgpu/shader/execution/exp2.bin": "836a1e66",
+  "webgpu/shader/execution/faceForward.bin": "366e24b3",
+  "webgpu/shader/execution/floor.bin": "91015364",
+  "webgpu/shader/execution/fma.bin": "a6c54ea7",
+  "webgpu/shader/execution/fract.bin": "5fc52848",
+  "webgpu/shader/execution/frexp.bin": "51292173",
+  "webgpu/shader/execution/inverseSqrt.bin": "b9b0ae99",
+  "webgpu/shader/execution/ldexp.bin": "ea263df5",
+  "webgpu/shader/execution/length.bin": "7976e258",
+  "webgpu/shader/execution/log.bin": "9d5760d3",
+  "webgpu/shader/execution/log2.bin": "a25cf8fb",
+  "webgpu/shader/execution/max.bin": "ae846d",
+  "webgpu/shader/execution/min.bin": "8d5bf419",
+  "webgpu/shader/execution/mix.bin": "ec9b70a5",
+  "webgpu/shader/execution/modf.bin": "e715d023",
+  "webgpu/shader/execution/normalize.bin": "fd2b0e38",
+  "webgpu/shader/execution/pack2x16float.bin": "9f7090b0",
+  "webgpu/shader/execution/pow.bin": "8ef53194",
+  "webgpu/shader/execution/quantizeToF16.bin": "898deab3",
+  "webgpu/shader/execution/radians.bin": "402b8cfc",
+  "webgpu/shader/execution/reflect.bin": "dd6092d2",
+  "webgpu/shader/execution/refract.bin": "fcb87a99",
+  "webgpu/shader/execution/round.bin": "784dff70",
+  "webgpu/shader/execution/saturate.bin": "5b1a465",
+  "webgpu/shader/execution/sign.bin": "15e32305",
+  "webgpu/shader/execution/sin.bin": "7d9f3bf6",
+  "webgpu/shader/execution/sinh.bin": "74c0da74",
+  "webgpu/shader/execution/smoothstep.bin": "8934b7cf",
+  "webgpu/shader/execution/sqrt.bin": "fca89209",
+  "webgpu/shader/execution/step.bin": "71afbcf9",
+  "webgpu/shader/execution/tan.bin": "ea17d347",
+  "webgpu/shader/execution/tanh.bin": "c63e2ccf",
+  "webgpu/shader/execution/transpose.bin": "320af848",
+  "webgpu/shader/execution/trunc.bin": "5d2eced1",
+  "webgpu/shader/execution/unpack2x16float.bin": "d8e95aa8",
+  "webgpu/shader/execution/unpack2x16snorm.bin": "c09c4961",
+  "webgpu/shader/execution/unpack2x16unorm.bin": "fb72f053",
+  "webgpu/shader/execution/unpack4x8snorm.bin": "2b203d72",
+  "webgpu/shader/execution/unpack4x8unorm.bin": "1908b0bc",
+  "webgpu/shader/execution/unary/af_arithmetic.bin": "4fb1cabc",
+  "webgpu/shader/execution/unary/af_assignment.bin": "a6c21fc6",
   "webgpu/shader/execution/unary/bool_conversion.bin": "dd71f171",
-  "webgpu/shader/execution/unary/f16_arithmetic.bin": "1d6b84ef",
-  "webgpu/shader/execution/unary/f16_conversion.bin": "406aff92",
-  "webgpu/shader/execution/unary/f32_arithmetic.bin": "6d2c7f7b",
-  "webgpu/shader/execution/unary/f32_conversion.bin": "d7f9967f",
+  "webgpu/shader/execution/unary/f16_arithmetic.bin": "c2e491ce",
+  "webgpu/shader/execution/unary/f16_conversion.bin": "4da55ca6",
+  "webgpu/shader/execution/unary/f32_arithmetic.bin": "b4b7823e",
+  "webgpu/shader/execution/unary/f32_conversion.bin": "1285037c",
   "webgpu/shader/execution/unary/i32_arithmetic.bin": "c69716e2",
   "webgpu/shader/execution/unary/i32_conversion.bin": "83218e69",
   "webgpu/shader/execution/unary/u32_conversion.bin": "8f5bad00",
   "webgpu/shader/execution/unary/ai_assignment.bin": "c7e6ac33",
-  "webgpu/shader/execution/binary/ai_arithmetic.bin": "81c11ec2",
+  "webgpu/shader/execution/binary/ai_arithmetic.bin": "fe312677",
   "webgpu/shader/execution/unary/ai_arithmetic.bin": "3d27dc97",
-  "webgpu/shader/execution/binary/af_matrix_matrix_multiplication.bin": "df23d63a",
-  "webgpu/shader/execution/binary/af_matrix_scalar_multiplication.bin": "718ef50",
-  "webgpu/shader/execution/binary/af_matrix_vector_multiplication.bin": "495e66cf"
+  "webgpu/shader/execution/binary/af_matrix_matrix_multiplication.bin": "e0d69ae6",
+  "webgpu/shader/execution/binary/af_matrix_scalar_multiplication.bin": "5347f7ef",
+  "webgpu/shader/execution/binary/af_matrix_vector_multiplication.bin": "79a9997"
 }
diff --git a/src/resources/cache/webgpu/shader/execution/binary/af_matrix_matrix_multiplication.bin b/src/resources/cache/webgpu/shader/execution/binary/af_matrix_matrix_multiplication.bin
diff --git a/src/resources/cache/webgpu/shader/execution/binary/af_matrix_scalar_multiplication.bin b/src/resources/cache/webgpu/shader/execution/binary/af_matrix_scalar_multiplication.bin
diff --git a/src/resources/cache/webgpu/shader/execution/binary/af_matrix_vector_multiplication.bin b/src/resources/cache/webgpu/shader/execution/binary/af_matrix_vector_multiplication.bin
diff --git a/src/webgpu/shader/execution/expression/binary/af_matrix_matrix_multiplication.cache.ts b/src/webgpu/shader/execution/expression/binary/af_matrix_matrix_multiplication.cache.ts
@@ -1,16 +1,16 @@
 import { FP } from '../../../../util/floating_point.js';
 import { sparseMatrixF64Range } from '../../../../util/math.js';
-import { StochasticFilter } from '../../../../util/stochastic_filter.js';
+import { selectNCases } from '../case.js';
 import { makeCaseCache } from '../case_cache.js';
 
-const sf = new StochasticFilter(0);
 // Cases: matKxR_matCxK
 const mat_mat_cases = ([2, 3, 4] as const)
   .flatMap(k =>
     ([2, 3, 4] as const).flatMap(cols =>
       ([2, 3, 4] as const).map(rows => ({
         [`mat${k}x${rows}_mat${cols}x${k}`]: () => {
-          return sf.filter(
+          return selectNCases(
+            50,
             FP.abstract.generateMatrixPairToMatrixCases(
               sparseMatrixF64Range(k, rows),
               sparseMatrixF64Range(cols, k),

diff --git a/src/webgpu/shader/execution/expression/binary/af_matrix_scalar_multiplication.cache.ts b/src/webgpu/shader/execution/expression/binary/af_matrix_scalar_multiplication.cache.ts
@@ -1,17 +1,21 @@
 import { FP } from '../../../../util/floating_point.js';
 import { sparseMatrixF64Range, sparseScalarF64Range } from '../../../../util/math.js';
+import { selectNCases } from '../case.js';
 import { makeCaseCache } from '../case_cache.js';
 
 // Cases: matCxR_scalar
 const mat_scalar_cases = ([2, 3, 4] as const)
   .flatMap(cols =>
     ([2, 3, 4] as const).map(rows => ({
       [`mat${cols}x${rows}_scalar`]: () => {
-        return FP.abstract.generateMatrixScalarToMatrixCases(
-          sparseMatrixF64Range(cols, rows),
-          sparseScalarF64Range(),
-          'finite',
-          FP.abstract.multiplicationMatrixScalarInterval
+        return selectNCases(
+          50,
+          FP.abstract.generateMatrixScalarToMatrixCases(
+            sparseMatrixF64Range(cols, rows),
+            sparseScalarF64Range(),
+            'finite',
+            FP.abstract.multiplicationMatrixScalarInterval
+          )
         );
       },
     }))
@@ -23,11 +27,14 @@ const scalar_mat_cases = ([2, 3, 4] as const)
   .flatMap(cols =>
     ([2, 3, 4] as const).map(rows => ({
       [`scalar_mat${cols}x${rows}`]: () => {
-        return FP.abstract.generateScalarMatrixToMatrixCases(
-          sparseScalarF64Range(),
-          sparseMatrixF64Range(cols, rows),
-          'finite',
-          FP.abstract.multiplicationScalarMatrixInterval
+        return selectNCases(
+          50,
+          FP.abstract.generateScalarMatrixToMatrixCases(
+            sparseScalarF64Range(),
+            sparseMatrixF64Range(cols, rows),
+            'finite',
+            FP.abstract.multiplicationScalarMatrixInterval
+          )
         );
       },
     }))

diff --git a/src/webgpu/shader/execution/expression/binary/af_matrix_vector_multiplication.cache.ts b/src/webgpu/shader/execution/expression/binary/af_matrix_vector_multiplication.cache.ts
@@ -1,17 +1,21 @@
 import { FP } from '../../../../util/floating_point.js';
 import { sparseMatrixF64Range, sparseVectorF64Range } from '../../../../util/math.js';
+import { selectNCases } from '../case.js';
 import { makeCaseCache } from '../case_cache.js';
 
 // Cases: matCxR_vecC
 const mat_vec_cases = ([2, 3, 4] as const)
   .flatMap(cols =>
     ([2, 3, 4] as const).map(rows => ({
       [`mat${cols}x${rows}_vec${cols}`]: () => {
-        return FP.abstract.generateMatrixVectorToVectorCases(
-          sparseMatrixF64Range(cols, rows),
-          sparseVectorF64Range(cols),
-          'finite',
-          FP.abstract.multiplicationMatrixVectorInterval
+        return selectNCases(
+          50,
+          FP.abstract.generateMatrixVectorToVectorCases(
+            sparseMatrixF64Range(cols, rows),
+            sparseVectorF64Range(cols),
+            'finite',
+            FP.abstract.multiplicationMatrixVectorInterval
+          )
         );
       },
     }))
@@ -23,11 +27,14 @@ const vec_mat_cases = ([2, 3, 4] as const)
   .flatMap(rows =>
     ([2, 3, 4] as const).map(cols => ({
       [`vec${rows}_mat${cols}x${rows}`]: () => {
-        return FP.abstract.generateVectorMatrixToVectorCases(
-          sparseVectorF64Range(rows),
-          sparseMatrixF64Range(cols, rows),
-          'finite',
-          FP.abstract.multiplicationVectorMatrixInterval
+        return selectNCases(
+          50,
+          FP.abstract.generateVectorMatrixToVectorCases(
+            sparseVectorF64Range(rows),
+            sparseMatrixF64Range(cols, rows),
+            'finite',
+            FP.abstract.multiplicationVectorMatrixInterval
+          )
         );
       },
     }))

diff --git a/src/webgpu/shader/execution/expression/case.ts b/src/webgpu/shader/execution/expression/case.ts
@@ -1,11 +1,13 @@
+import { crc32 } from '../../../../common/util/crc32.js';
 import { ROArrayArray } from '../../../../common/util/types.js';
-import { ScalarBuilder, Value, Vector, i32, u32, abstractInt } from '../../../util/conversion.js';
+import { assert } from '../../../../common/util/util.js';
+import { abstractInt, i32, ScalarBuilder, u32, Value, Vector } from '../../../util/conversion.js';
 import {
-  QuantizeFunc,
   cartesianProduct,
+  QuantizeFunc,
   quantizeToI32,
-  quantizeToU32,
   quantizeToI64,
+  quantizeToU32,
 } from '../../../util/math.js';
 
 import { Expectation } from './expectation.js';
@@ -25,6 +27,41 @@ export type Case = {
 /** CaseList is a list of Cases */
 export type CaseList = Array<Case>;
 
+/**
+ * Filters a given set of Cases down to a target number of cases by
+ * randomly selecting which Cases to return.
+ *
+ * The selection algorithm is deterministic and stable for a case's
+ * inputs.
+ *
+ * This means that if a specific case is selected is not affected by the
+ * presence of other cases in the list, so in theory it is possible to create a
+ * pathological set of cases such that all or not of the cases are selected
+ * in spite of the target number.
+ *
+ * This is a trade-off from guaranteeing stability of the selected cases over
+ * small changes, so the target number of cases is more of a suggestion. It is
+ * still guaranteed that if you set n0 < n1, then the invocation with n0 will
+ * return at most the number of cases that n1 does, it just isn't guaranteed to
+ * be less.
+ *
+ * @param n number of cases targeted be returned. Expected to be a positive
+ *          integer. If equal or greater than the number of cases, then all the
+ *          cases are returned. 0 is not allowed, since it is likely a
+ *          programming error, because if the caller intentionally wants 0
+ *          items, they can just use [].
+ * @param cases list of Cases to be selected from.
+ */
+export function selectNCases(n: number, cases: CaseList): CaseList {
+  assert(n > 0 && Math.round(n) === n, `n ${n} is expected to be a positive integer`);
+  const count = cases.length;
+  if (n >= count) {
+    return cases;
+  }
+
+  return cases.filter(c => n * (0xffff_ffff / count) > crc32(c.input.toString()));
+}
+
 /**
  * A function that performs a binary operation on x and y, and returns the
  * expected result.