zstd: Big speedup on small dictionary encodes (#345)

All credit goes to @tony2001

As shown in #344 the speed of small dictionary compression tasks (< 32K) can be improved significantly by keeping track of the state of the hash table.

This effectively implements #344 but avoids a penalty for non-dictionary encodes and extends the functionality to the "better" compression mode as well.

This change will also make it easier to [remove the copy of the literal dictionary](https://github.com/klauspost/compress/blob/a0dc84a8cf242dde7e21f8aba26126ca4621ff8c/zstd/enc_base.go#L171) every time an encode starts and have specialized code to deal with this.

```
benchmark                                                                     old ns/op     new ns/op     delta
BenchmarkEncodeAllDict0_1024/length-19-level-fastest-dict-1-32                5729          870           -84.82%
BenchmarkEncodeAllDict0_1024/length-19-level-default-dict-1-32                59694         2115          -96.46%
BenchmarkEncodeAllDict0_1024/length-19-level-better-dict-1-32                 197183        2454          -98.76%
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1-32                 5596          600           -89.28%
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1-32                 59342         1222          -97.94%
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1-32                  194466        1958          -98.99%
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1-32               13343         13132         -1.58%
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1-32               72651         33988         -53.22%
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1-32                211509        22635         -89.30%
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1-32               12190         10318         -15.36%
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1-32               71443         28580         -60.00%
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1-32                213304        17914         -91.60%
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#01-32              5582          595           -89.33%
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#01-32              58721         1221          -97.92%
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#01-32               196875        1963          -99.00%
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#01-32            13260         13132         -0.97%
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#01-32            71944         33896         -52.89%
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#01-32             207200        22533         -89.12%
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#01-32            12218         10295         -15.74%
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#01-32            69490         28531         -58.94%
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#01-32             205039        18020         -91.21%
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#02-32              5579          599           -89.26%
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#02-32              60810         1228          -97.98%
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#02-32               198740        1953          -99.02%
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#02-32            13352         13128         -1.68%
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#02-32            72544         33887         -53.29%
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#02-32             213331        22516         -89.45%
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#02-32            12204         10299         -15.61%
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#02-32            69317         28421         -59.00%
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#02-32             207613        17917         -91.37%
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#03-32              5542          600           -89.17%
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#03-32              59132         1218          -97.94%
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#03-32               196451        1952          -99.01%
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#03-32            13319         13112         -1.55%
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#03-32            70234         33843         -51.81%
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#03-32             209384        22447         -89.28%
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#03-32            12285         10297         -16.18%
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#03-32            71972         28585         -60.28%
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#03-32             215483        17902         -91.69%
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1-32           16508         16221         -1.74%
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1-32           83569         41344         -50.53%
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1-32            220306        39384         -82.12%
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1-32           41125         40975         -0.36%
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1-32           163203        77122         -52.74%
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1-32            318789        137116        -56.99%
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#01-32        16586         16294         -1.76%
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#01-32        82607         41120         -50.22%
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#01-32         219278        39179         -82.13%
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#01-32        42267         41093         -2.78%
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#01-32        164353        76905         -53.21%
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#01-32         327857        136501        -58.37%
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#02-32        16554         16177         -2.28%
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#02-32        83337         41239         -50.52%
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#02-32         226392        39385         -82.60%
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#02-32        41175         40834         -0.83%
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#02-32        160614        77318         -51.86%
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#02-32         313359        136739        -56.36%
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#03-32        16413         16274         -0.85%
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#03-32        81907         41151         -49.76%
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#03-32         222585        39181         -82.40%
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#03-32        41232         40978         -0.62%
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#03-32        159086        77235         -51.45%
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#03-32         309822        136600        -55.91%
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1-32         55120         55056         -0.12%
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1-32         291966        132353        -54.67%
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1-32          467914        206802        -55.80%
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#01-32      53770         54785         +1.89%
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#01-32      291053        130230        -55.26%
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#01-32       476829        205292        -56.95%
BenchmarkEncodeAllDict8192_16384/length-9024-level-fastest-dict-1-32          31805         31891         +0.27%
BenchmarkEncodeAllDict8192_16384/length-9024-level-default-dict-1-32          116904        61027         -47.80%
BenchmarkEncodeAllDict8192_16384/length-9024-level-better-dict-1-32           260057        95128         -63.42%
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#02-32      54833         54341         -0.90%
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#02-32      291523        131595        -54.86%
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#02-32       467178        206408        -55.82%
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#03-32      54431         54289         -0.26%
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#03-32      291092        130441        -55.19%
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#03-32       476490        205606        -56.85%
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1-32        245211        243965        -0.51%
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1-32        817566        822310        +0.58%
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1-32         1258889       590281        -53.11%
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#01-32     242203        241662        -0.22%
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#01-32     812895        818005        +0.63%
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#01-32      1265187       590826        -53.30%
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#02-32     242602        241849        -0.31%
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#02-32     828540        819250        -1.12%
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#02-32      1286233       586918        -54.37%
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#03-32     245593        244559        -0.42%
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#03-32     813931        819203        +0.65%
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#03-32      1272813       581714        -54.30%
BenchmarkEncodeAllDict16384_65536/length-20000-level-fastest-dict-1-32        18972         18733         -1.26%
BenchmarkEncodeAllDict16384_65536/length-20000-level-default-dict-1-32        75984         39850         -47.55%
BenchmarkEncodeAllDict16384_65536/length-20000-level-better-dict-1-32         213173        27825         -86.95%
BenchmarkEncodeAllDict65536_0/length-210569-level-fastest-dict-1-32           1070089       1055243       -1.39%
BenchmarkEncodeAllDict65536_0/length-210569-level-default-dict-1-32           1780011       1819554       +2.22%
BenchmarkEncodeAllDict65536_0/length-210569-level-better-dict-1-32            2785437       1631976       -41.41%
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1-32           500568        499781        -0.16%
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1-32           1036024       1076927       +3.95%
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1-32            1740181       859317        -50.62%
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1-32            410671        405122        -1.35%
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1-32            1025429       1025611       +0.02%
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1-32             1584230       739134        -53.34%
BenchmarkEncodeAllDict65536_0/length-210569-level-fastest-dict-1#01-32        1054258       1048012       -0.59%
BenchmarkEncodeAllDict65536_0/length-210569-level-default-dict-1#01-32        1756825       1810346       +3.05%
BenchmarkEncodeAllDict65536_0/length-210569-level-better-dict-1#01-32         2816869       1659755       -41.08%
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#01-32        498201        500382        +0.44%
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#01-32        1045296       1075033       +2.84%
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#01-32         1772563       855280        -51.75%
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#01-32         411487        404032        -1.81%
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#01-32         1009682       1023147       +1.33%
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#01-32          1588776       728182        -54.17%
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#02-32        501487        498564        -0.58%
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#02-32        1037744       1074253       +3.52%
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#02-32         1753509       859959        -50.96%
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#02-32         407233        403579        -0.90%
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#02-32         1013906       1026835       +1.28%
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#02-32          1591512       731027        -54.07%
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#03-32        500983        495842        -1.03%
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#03-32        1046435       1075070       +2.74%
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#03-32         1760434       860257        -51.13%
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#03-32         409099        405108        -0.98%
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#03-32         1011372       1021036       +0.96%
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#03-32          1572944       731780        -53.48%

benchmark                                                                     old MB/s     new MB/s     speedup
BenchmarkEncodeAllDict0_1024/length-19-level-fastest-dict-1-32                3.32         21.84        6.58x
BenchmarkEncodeAllDict0_1024/length-19-level-default-dict-1-32                0.32         8.98         28.06x
BenchmarkEncodeAllDict0_1024/length-19-level-better-dict-1-32                 0.10         7.74         77.40x
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1-32                 0.89         8.34         9.37x
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1-32                 0.08         4.09         51.12x
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1-32                  0.03         2.55         85.00x
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1-32               49.39        50.18        1.02x
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1-32               9.07         19.39        2.14x
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1-32                3.12         29.11        9.33x
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1-32               14.27        16.86        1.18x
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1-32               2.44         6.09         2.50x
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1-32                0.82         9.71         11.84x
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#01-32              0.90         8.40         9.33x
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#01-32              0.09         4.10         45.56x
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#01-32               0.03         2.55         85.00x
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#01-32            49.70        50.18        1.01x
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#01-32            9.16         19.44        2.12x
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#01-32             3.18         29.25        9.20x
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#01-32            14.24        16.90        1.19x
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#01-32            2.50         6.10         2.44x
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#01-32             0.85         9.66         11.36x
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#02-32              0.90         8.35         9.28x
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#02-32              0.08         4.07         50.88x
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#02-32               0.03         2.56         85.33x
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#02-32            49.36        50.20        1.02x
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#02-32            9.08         19.45        2.14x
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#02-32             3.09         29.27        9.47x
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#02-32            14.26        16.90        1.19x
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#02-32            2.51         6.12         2.44x
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#02-32             0.84         9.71         11.56x
BenchmarkEncodeAllDict0_1024/length-5-level-fastest-dict-1#03-32              0.90         8.33         9.26x
BenchmarkEncodeAllDict0_1024/length-5-level-default-dict-1#03-32              0.08         4.11         51.38x
BenchmarkEncodeAllDict0_1024/length-5-level-better-dict-1#03-32               0.03         2.56         85.33x
BenchmarkEncodeAllDict0_1024/length-659-level-fastest-dict-1#03-32            49.48        50.26        1.02x
BenchmarkEncodeAllDict0_1024/length-659-level-default-dict-1#03-32            9.38         19.47        2.08x
BenchmarkEncodeAllDict0_1024/length-659-level-better-dict-1#03-32             3.15         29.36        9.32x
BenchmarkEncodeAllDict0_1024/length-174-level-fastest-dict-1#03-32            14.16        16.90        1.19x
BenchmarkEncodeAllDict0_1024/length-174-level-default-dict-1#03-32            2.42         6.09         2.52x
BenchmarkEncodeAllDict0_1024/length-174-level-better-dict-1#03-32             0.81         9.72         12.00x
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1-32           65.18        66.33        1.02x
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1-32           12.88        26.03        2.02x
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1-32            4.88         27.32        5.60x
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1-32           142.78       143.31       1.00x
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1-32           35.98        76.14        2.12x
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1-32            18.42        42.82        2.32x
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#01-32        64.88        66.04        1.02x
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#01-32        13.03        26.17        2.01x
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#01-32         4.91         27.46        5.59x
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#01-32        138.93       142.90       1.03x
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#01-32        35.73        76.35        2.14x
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#01-32         17.91        43.02        2.40x
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#02-32        65.00        66.51        1.02x
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#02-32        12.91        26.09        2.02x
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#02-32         4.75         27.32        5.75x
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#02-32        142.61       143.80       1.01x
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#02-32        36.56        75.95        2.08x
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#02-32         18.74        42.94        2.29x
BenchmarkEncodeAllDict1024_8192/length-1076-level-fastest-dict-1#03-32        65.56        66.12        1.01x
BenchmarkEncodeAllDict1024_8192/length-1076-level-default-dict-1#03-32        13.14        26.15        1.99x
BenchmarkEncodeAllDict1024_8192/length-1076-level-better-dict-1#03-32         4.83         27.46        5.69x
BenchmarkEncodeAllDict1024_8192/length-5872-level-fastest-dict-1#03-32        142.41       143.30       1.01x
BenchmarkEncodeAllDict1024_8192/length-5872-level-default-dict-1#03-32        36.91        76.03        2.06x
BenchmarkEncodeAllDict1024_8192/length-5872-level-better-dict-1#03-32         18.95        42.99        2.27x
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1-32         220.08       220.34       1.00x
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1-32         41.55        91.66        2.21x
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1-32          25.93        58.66        2.26x
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#01-32      225.61       221.43       0.98x
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#01-32      41.68        93.15        2.23x
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#01-32       25.44        59.09        2.32x
BenchmarkEncodeAllDict8192_16384/length-9024-level-fastest-dict-1-32          283.73       282.97       1.00x
BenchmarkEncodeAllDict8192_16384/length-9024-level-default-dict-1-32          77.19        147.87       1.92x
BenchmarkEncodeAllDict8192_16384/length-9024-level-better-dict-1-32           34.70        94.86        2.73x
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#02-32      221.23       223.24       1.01x
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#02-32      41.61        92.18        2.22x
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#02-32       25.97        58.77        2.26x
BenchmarkEncodeAllDict8192_16384/length-12131-level-fastest-dict-1#03-32      222.87       223.45       1.00x
BenchmarkEncodeAllDict8192_16384/length-12131-level-default-dict-1#03-32      41.67        93.00        2.23x
BenchmarkEncodeAllDict8192_16384/length-12131-level-better-dict-1#03-32       25.46        59.00        2.32x
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1-32        243.44       244.69       1.01x
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1-32        73.02        72.59        0.99x
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1-32         47.42        101.13       2.13x
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#01-32     246.47       247.02       1.00x
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#01-32     73.44        72.98        0.99x
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#01-32      47.18        101.04       2.14x
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#02-32     246.06       246.83       1.00x
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#02-32     72.05        72.87        1.01x
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#02-32      46.41        101.71       2.19x
BenchmarkEncodeAllDict16384_65536/length-59695-level-fastest-dict-1#03-32     243.06       244.09       1.00x
BenchmarkEncodeAllDict16384_65536/length-59695-level-default-dict-1#03-32     73.34        72.87        0.99x
BenchmarkEncodeAllDict16384_65536/length-59695-level-better-dict-1#03-32      46.90        102.62       2.19x
BenchmarkEncodeAllDict16384_65536/length-20000-level-fastest-dict-1-32        1054.19      1067.64      1.01x
BenchmarkEncodeAllDict16384_65536/length-20000-level-default-dict-1-32        263.21       501.88       1.91x
BenchmarkEncodeAllDict16384_65536/length-20000-level-better-dict-1-32         93.82        718.77       7.66x
BenchmarkEncodeAllDict65536_0/length-210569-level-fastest-dict-1-32           196.78       199.55       1.01x
BenchmarkEncodeAllDict65536_0/length-210569-level-default-dict-1-32           118.30       115.73       0.98x
BenchmarkEncodeAllDict65536_0/length-210569-level-better-dict-1-32            75.60        129.03       1.71x
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1-32           204.98       205.30       1.00x
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1-32           99.04        95.28        0.96x
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1-32            58.96        119.40       2.03x
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1-32            165.61       167.88       1.01x
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1-32            66.33        66.31        1.00x
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1-32             42.93        92.02        2.14x
BenchmarkEncodeAllDict65536_0/length-210569-level-fastest-dict-1#01-32        199.73       200.92       1.01x
BenchmarkEncodeAllDict65536_0/length-210569-level-default-dict-1#01-32        119.86       116.31       0.97x
BenchmarkEncodeAllDict65536_0/length-210569-level-better-dict-1#01-32         74.75        126.87       1.70x
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#01-32        205.95       205.05       1.00x
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#01-32        98.16        95.44        0.97x
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#01-32         57.89        119.97       2.07x
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#01-32         165.29       168.34       1.02x
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#01-32         67.36        66.47        0.99x
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#01-32          42.81        93.40        2.18x
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#02-32        204.60       205.80       1.01x
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#02-32        98.87        95.51        0.97x
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#02-32         58.51        119.31       2.04x
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#02-32         167.01       168.52       1.01x
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#02-32         67.08        66.24        0.99x
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#02-32          42.73        93.04        2.18x
BenchmarkEncodeAllDict65536_0/length-102605-level-fastest-dict-1#03-32        204.81       206.93       1.01x
BenchmarkEncodeAllDict65536_0/length-102605-level-default-dict-1#03-32        98.05        95.44        0.97x
BenchmarkEncodeAllDict65536_0/length-102605-level-better-dict-1#03-32         58.28        119.27       2.05x
BenchmarkEncodeAllDict65536_0/length-68013-level-fastest-dict-1#03-32         166.25       167.89       1.01x
BenchmarkEncodeAllDict65536_0/length-68013-level-default-dict-1#03-32         67.25        66.61        0.99x
BenchmarkEncodeAllDict65536_0/length-68013-level-better-dict-1#03-32          43.24        92.94        2.15x 
 ```

zstd/dict_test.go

@@ -218,7 +218,7 @@ func TestEncoder_SmallDict(t *testing.T) {
 	}
 }
 
-func BenchmarkEncodeAllDict(b *testing.B) {
+func benchmarkEncodeAllLimitedBySize(b *testing.B, lowerLimit int, upperLimit int) {
 	fn := "testdata/dict-tests-small.zip"
 	data, err := ioutil.ReadFile(fn)
 	t := testing.TB(b)
@@ -232,7 +232,6 @@ func BenchmarkEncodeAllDict(b *testing.B) {
 	}
 	var dicts [][]byte
 	var encs []*Encoder
-	var noDictEncs []*Encoder
 	var encNames []string
 
 	for _, tt := range zr.File {
@@ -251,32 +250,25 @@ func BenchmarkEncodeAllDict(b *testing.B) {
 			}
 			dicts = append(dicts, in)
 			for level := SpeedFastest; level < speedLast; level++ {
-				enc, err := NewWriter(nil, WithEncoderConcurrency(1), WithEncoderDict(in), WithEncoderLevel(level), WithWindowSize(1<<17))
+				enc, err := NewWriter(nil, WithEncoderDict(in), WithEncoderLevel(level))
 				if err != nil {
 					t.Fatal(err)
 				}
 				encs = append(encs, enc)
 				encNames = append(encNames, fmt.Sprint("level-", level.String(), "-dict-", len(dicts)))
-
-				enc, err = NewWriter(nil, WithEncoderConcurrency(1), WithEncoderLevel(level), WithWindowSize(1<<17))
-				if err != nil {
-					t.Fatal(err)
-				}
-				noDictEncs = append(noDictEncs, enc)
 			}
 		}()
 	}
+	const nPer = int(speedLast - SpeedFastest)
 	dec, err := NewReader(nil, WithDecoderConcurrency(1), WithDecoderDicts(dicts...))
 	if err != nil {
 		t.Fatal(err)
 		return
 	}
 	defer dec.Close()
 
-	for i, tt := range zr.File {
-		if i == 5 {
-			break
-		}
+	tested := make(map[int]struct{})
+	for j, tt := range zr.File {
 		if !strings.HasSuffix(tt.Name, ".zst") {
 			continue
 		}
@@ -293,26 +285,64 @@ func BenchmarkEncodeAllDict(b *testing.B) {
 		if err != nil {
 			t.Fatal(err)
 		}
+
+		// Only test each size once
+		if _, ok := tested[len(decoded)]; ok {
+			continue
+		}
+		tested[len(decoded)] = struct{}{}
+
+		if len(decoded) < lowerLimit {
+			continue
+		}
+
+		if upperLimit > 0 && len(decoded) > upperLimit {
+			continue
+		}
+
 		for i := range encs {
-			// Only do 1 dict (3 encoders) for now.
-			if i == 3 {
+			// Only do 1 dict (4 encoders) for now.
+			if i == nPer-1 {
 				break
 			}
 			// Attempt to compress with all dicts
-			var dst []byte
-			enc := encs[i]
-			b.Run(fmt.Sprintf("length-%d-%s", len(decoded), encNames[i]), func(b *testing.B) {
-				b.SetBytes(int64(len(decoded)))
-				b.ResetTimer()
-				b.ReportAllocs()
-				for i := 0; i < b.N; i++ {
-					dst = enc.EncodeAll(decoded, dst[:0])
-				}
+			encIdx := (i + j*nPer) % len(encs)
+			enc := encs[encIdx]
+			b.Run(fmt.Sprintf("length-%d-%s", len(decoded), encNames[encIdx]), func(b *testing.B) {
+				b.RunParallel(func(pb *testing.PB) {
+					dst := make([]byte, 0, len(decoded)+10)
+					b.SetBytes(int64(len(decoded)))
+					b.ResetTimer()
+					b.ReportAllocs()
+					for pb.Next() {
+						dst = enc.EncodeAll(decoded, dst[:0])
+					}
+				})
 			})
 		}
 	}
 }
 
+func BenchmarkEncodeAllDict0_1024(b *testing.B) {
+	benchmarkEncodeAllLimitedBySize(b, 0, 1024)
+}
+
+func BenchmarkEncodeAllDict1024_8192(b *testing.B) {
+	benchmarkEncodeAllLimitedBySize(b, 1024, 8192)
+}
+
+func BenchmarkEncodeAllDict8192_16384(b *testing.B) {
+	benchmarkEncodeAllLimitedBySize(b, 8192, 16384)
+}
+
+func BenchmarkEncodeAllDict16384_65536(b *testing.B) {
+	benchmarkEncodeAllLimitedBySize(b, 16384, 65536)
+}
+
+func BenchmarkEncodeAllDict65536_0(b *testing.B) {
+	benchmarkEncodeAllLimitedBySize(b, 65536, 0)
+}
+
 func TestDecoder_MoreDicts(t *testing.T) {
 	// All files have CRC
 	// https://files.klauspost.com/compress/zstd-dict-tests.zip

zstd/enc_base.go

@@ -7,6 +7,10 @@ import (
 	"github.com/klauspost/compress/zstd/internal/xxhash"
 )
 
+const (
+	dictShardBits = 6
+)
+
 type fastBase struct {
 	// cur is the offset at the start of hist
 	cur int32