From d2bbf06936c7a519d31555d845d964b00ee63503 Mon Sep 17 00:00:00 2001 From: Dmitrii Dolgov <9erthalion6@gmail.com> Date: Mon, 13 Apr 2026 20:49:11 +0200 Subject: [PATCH v1 2/2] Add delays from geometric distribution Introduce delays between IOs following a geometric distribution (a discrete analog of exponential distribution) using ziggurat algorithm. --- contrib/io_limit/io_limit.c | 47 +++- contrib/io_limit/ziggurat.h | 457 ++++++++++++++++++++++++++++++++++++ 2 files changed, 503 insertions(+), 1 deletion(-) create mode 100644 contrib/io_limit/ziggurat.h diff --git a/contrib/io_limit/io_limit.c b/contrib/io_limit/io_limit.c index fa2ec6f1ff2..7e36af03138 100644 --- a/contrib/io_limit/io_limit.c +++ b/contrib/io_limit/io_limit.c @@ -8,11 +8,13 @@ #include "storage/lwlock.h" #include "storage/shmem.h" #include "utils/guc.h" +#include "ziggurat.h" /* GUCs. */ static int io_limit_ios_per_second = 0; static int io_limit_read_per_second = 0; static int io_limit_write_per_second = 0; +static int io_limit_mean_delay = 0; typedef struct io_limit_control_data { @@ -29,6 +31,8 @@ typedef struct io_limit_control_data int op_ns; int read_block_ns; int write_block_ns; + + double ios_probability; } io_limit_control_data; static io_limit_control_data * io_limit_control; @@ -39,6 +43,7 @@ static void io_limit_shmem_init(void *arg); static void assign_io_limit_ios_per_second(int newval, void *extra); static void assign_io_limit_read_per_second(int newval, void *extra); static void assign_io_limit_write_per_second(int newval, void *extra); +static void assign_io_mean(int newval, void *extra); static const char *show_io_limit_ios_per_second(void); static const char *show_io_limit_read_per_second(void); static const char *show_io_limit_write_per_second(void); @@ -95,6 +100,18 @@ _PG_init(void) NULL, assign_io_limit_write_per_second, show_io_limit_write_per_second); + DefineCustomIntVariable("io_limit.mean_delay", + "For sampling delays from the geometric distribution, " + "mean delay in ns (1/p).", + "If set to zero, no random sampling is performed.", + &io_limit_mean_delay, + 0, + 0, INT_MAX, + PGC_USERSET, + 0, + NULL, + assign_io_mean, + show_io_limit_ios_per_second); MarkGUCPrefixReserved("io_limit"); RegisterShmemCallbacks(&io_limit_shmem_callbacks); @@ -122,6 +139,8 @@ io_limit_shmem_init(void *arg) assign_io_limit_ios_per_second(io_limit_ios_per_second, NULL); assign_io_limit_read_per_second(io_limit_read_per_second, NULL); assign_io_limit_write_per_second(io_limit_write_per_second, NULL); + + assign_io_mean(io_limit_mean_delay, NULL); } static void @@ -136,7 +155,25 @@ assign_io_limit(int *wait_ns, int per_second) io_limit_control->enabled = io_limit_control->op_ns > 0 || io_limit_control->read_block_ns > 0 || - io_limit_control->write_block_ns > 0; + io_limit_control->write_block_ns > 0 || + io_limit_control->ios_probability > 0; + LWLockRelease(&io_limit_control->lock); +} + +static void +assign_io_mean(int newval, void *extra) +{ + /* Ignore call from _PG_init() before ready. */ + if (!io_limit_control) + return; + + LWLockAcquire(&io_limit_control->lock, LW_EXCLUSIVE); + io_limit_control->ios_probability = 1.0 / (double) newval; + io_limit_control->enabled = + io_limit_control->op_ns > 0 || + io_limit_control->read_block_ns > 0 || + io_limit_control->write_block_ns > 0 || + io_limit_control->ios_probability > 0; LWLockRelease(&io_limit_control->lock); } @@ -251,10 +288,18 @@ io_limit_on_perform(PgAioHandle *ioh) int op_ns; int read_block_ns; int write_block_ns; + double ios_probability; if (!io_limit_control->enabled) return; + ios_probability = io_limit_control->ios_probability; + if (ios_probability) + { + int delay = random_geometric_inversion(io_limit_control->ios_probability); + io_limit_wait(&io_limit_control->op_next_ns, delay); + } + op_ns = io_limit_control->op_ns; if (op_ns) io_limit_wait(&io_limit_control->op_next_ns, op_ns); diff --git a/contrib/io_limit/ziggurat.h b/contrib/io_limit/ziggurat.h new file mode 100644 index 00000000000..61331d11676 --- /dev/null +++ b/contrib/io_limit/ziggurat.h @@ -0,0 +1,457 @@ +/*------------------------------------------------------------------------- + * + * ziggurat.h + * Constants and functionality for ziggurat method of generating random + * variables from: + * + * Marsaglia, George, and Wai Wan Tsang. "The ziggurat method for + * generating random variables." Journal of statistical software 5 + * (2000):1-7. + * + * Reference implementation is taken from numpy: + * numpy/random/src/distributions/ziggurat_constants.h + * + * Copyright (c) 2016-2026, PostgreSQL Global Development Group + * + * IDENTIFICATION + * contrib/io_limit/ziggurat.h + * + *------------------------------------------------------------------------- + */ +#ifndef _ZIGGURAT_H_ +#define _ZIGGURAT_H_ + +#include + +double std_uniform(); +double random_standard_exponential(); + +static const uint64_t ke_double[] = { + 0x001C5214272497C6, 0x0000000000000000, 0x00137D5BD79C317E, + 0x00186EF58E3F3C10, 0x001A9BB7320EB0AE, 0x001BD127F719447C, + 0x001C951D0F88651A, 0x001D1BFE2D5C3972, 0x001D7E5BD56B18B2, + 0x001DC934DD172C70, 0x001E0409DFAC9DC8, 0x001E337B71D47836, + 0x001E5A8B177CB7A2, 0x001E7B42096F046C, 0x001E970DAF08AE3E, + 0x001EAEF5B14EF09E, 0x001EC3BD07B46556, 0x001ED5F6F08799CE, + 0x001EE614AE6E5688, 0x001EF46ECA361CD0, 0x001F014B76DDD4A4, + 0x001F0CE313A796B6, 0x001F176369F1F77A, 0x001F20F20C452570, + 0x001F29AE1951A874, 0x001F31B18FB95532, 0x001F39125157C106, + 0x001F3FE2EB6E694C, 0x001F463332D788FA, 0x001F4C10BF1D3A0E, + 0x001F51874C5C3322, 0x001F56A109C3ECC0, 0x001F5B66D9099996, + 0x001F5FE08210D08C, 0x001F6414DD445772, 0x001F6809F6859678, + 0x001F6BC52A2B02E6, 0x001F6F4B3D32E4F4, 0x001F72A07190F13A, + 0x001F75C8974D09D6, 0x001F78C71B045CC0, 0x001F7B9F12413FF4, + 0x001F7E5346079F8A, 0x001F80E63BE21138, 0x001F835A3DAD9162, + 0x001F85B16056B912, 0x001F87ED89B24262, 0x001F8A10759374FA, + 0x001F8C1BBA3D39AC, 0x001F8E10CC45D04A, 0x001F8FF102013E16, + 0x001F91BD968358E0, 0x001F9377AC47AFD8, 0x001F95204F8B64DA, + 0x001F96B878633892, 0x001F98410C968892, 0x001F99BAE146BA80, + 0x001F9B26BC697F00, 0x001F9C85561B717A, 0x001F9DD759CFD802, + 0x001F9F1D6761A1CE, 0x001FA058140936C0, 0x001FA187EB3A3338, + 0x001FA2AD6F6BC4FC, 0x001FA3C91ACE0682, 0x001FA4DB5FEE6AA2, + 0x001FA5E4AA4D097C, 0x001FA6E55EE46782, 0x001FA7DDDCA51EC4, + 0x001FA8CE7CE6A874, 0x001FA9B793CE5FEE, 0x001FAA9970ADB858, + 0x001FAB745E588232, 0x001FAC48A3740584, 0x001FAD1682BF9FE8, + 0x001FADDE3B5782C0, 0x001FAEA008F21D6C, 0x001FAF5C2418B07E, + 0x001FB012C25B7A12, 0x001FB0C41681DFF4, 0x001FB17050B6F1FA, + 0x001FB2179EB2963A, 0x001FB2BA2BDFA84A, 0x001FB358217F4E18, + 0x001FB3F1A6C9BE0C, 0x001FB486E10CACD6, 0x001FB517F3C793FC, + 0x001FB5A500C5FDAA, 0x001FB62E2837FE58, 0x001FB6B388C9010A, + 0x001FB7353FB50798, 0x001FB7B368DC7DA8, 0x001FB82E1ED6BA08, + 0x001FB8A57B0347F6, 0x001FB919959A0F74, 0x001FB98A85BA7204, + 0x001FB9F861796F26, 0x001FBA633DEEE286, 0x001FBACB2F41EC16, + 0x001FBB3048B49144, 0x001FBB929CAEA4E2, 0x001FBBF23CC8029E, + 0x001FBC4F39D22994, 0x001FBCA9A3E140D4, 0x001FBD018A548F9E, + 0x001FBD56FBDE729C, 0x001FBDAA068BD66A, 0x001FBDFAB7CB3F40, + 0x001FBE491C7364DE, 0x001FBE9540C9695E, 0x001FBEDF3086B128, + 0x001FBF26F6DE6174, 0x001FBF6C9E828AE2, 0x001FBFB031A904C4, + 0x001FBFF1BA0FFDB0, 0x001FC03141024588, 0x001FC06ECF5B54B2, + 0x001FC0AA6D8B1426, 0x001FC0E42399698A, 0x001FC11BF9298A64, + 0x001FC151F57D1942, 0x001FC1861F770F4A, 0x001FC1B87D9E74B4, + 0x001FC1E91620EA42, 0x001FC217EED505DE, 0x001FC2450D3C83FE, + 0x001FC27076864FC2, 0x001FC29A2F90630E, 0x001FC2C23CE98046, + 0x001FC2E8A2D2C6B4, 0x001FC30D654122EC, 0x001FC33087DE9C0E, + 0x001FC3520E0B7EC6, 0x001FC371FADF66F8, 0x001FC390512A2886, + 0x001FC3AD137497FA, 0x001FC3C844013348, 0x001FC3E1E4CCAB40, + 0x001FC3F9F78E4DA8, 0x001FC4107DB85060, 0x001FC4257877FD68, + 0x001FC438E8B5BFC6, 0x001FC44ACF15112A, 0x001FC45B2BF447E8, + 0x001FC469FF6C4504, 0x001FC477495001B2, 0x001FC483092BFBB8, + 0x001FC48D3E457FF6, 0x001FC495E799D21A, 0x001FC49D03DD30B0, + 0x001FC4A29179B432, 0x001FC4A68E8E07FC, 0x001FC4A8F8EBFB8C, + 0x001FC4A9CE16EA9E, 0x001FC4A90B41FA34, 0x001FC4A6AD4E28A0, + 0x001FC4A2B0C82E74, 0x001FC49D11E62DE2, 0x001FC495CC852DF4, + 0x001FC48CDC265EC0, 0x001FC4823BEC237A, 0x001FC475E696DEE6, + 0x001FC467D6817E82, 0x001FC458059DC036, 0x001FC4466D702E20, + 0x001FC433070BCB98, 0x001FC41DCB0D6E0E, 0x001FC406B196BBF6, + 0x001FC3EDB248CB62, 0x001FC3D2C43E593C, 0x001FC3B5DE0591B4, + 0x001FC396F599614C, 0x001FC376005A4592, 0x001FC352F3069370, + 0x001FC32DC1B22818, 0x001FC3065FBD7888, 0x001FC2DCBFCBF262, + 0x001FC2B0D3B99F9E, 0x001FC2828C8FFCF0, 0x001FC251DA79F164, + 0x001FC21EACB6D39E, 0x001FC1E8F18C6756, 0x001FC1B09637BB3C, + 0x001FC17586DCCD10, 0x001FC137AE74D6B6, 0x001FC0F6F6BB2414, + 0x001FC0B348184DA4, 0x001FC06C898BAFF0, 0x001FC022A092F364, + 0x001FBFD5710F72B8, 0x001FBF84DD29488E, 0x001FBF30C52FC60A, + 0x001FBED907770CC6, 0x001FBE7D80327DDA, 0x001FBE1E094BA614, + 0x001FBDBA7A354408, 0x001FBD52A7B9F826, 0x001FBCE663C6201A, + 0x001FBC757D2C4DE4, 0x001FBBFFBF63B7AA, 0x001FBB84F23FE6A2, + 0x001FBB04D9A0D18C, 0x001FBA7F351A70AC, 0x001FB9F3BF92B618, + 0x001FB9622ED4ABFC, 0x001FB8CA33174A16, 0x001FB82B76765B54, + 0x001FB7859C5B895C, 0x001FB6D840D55594, 0x001FB622F7D96942, + 0x001FB5654C6F37E0, 0x001FB49EBFBF69D2, 0x001FB3CEC803E746, + 0x001FB2F4CF539C3E, 0x001FB21032442852, 0x001FB1203E5A9604, + 0x001FB0243042E1C2, 0x001FAF1B31C479A6, 0x001FAE045767E104, + 0x001FACDE9DBF2D72, 0x001FABA8E640060A, 0x001FAA61F399FF28, + 0x001FA908656F66A2, 0x001FA79AB3508D3C, 0x001FA61726D1F214, + 0x001FA47BD48BEA00, 0x001FA2C693C5C094, 0x001FA0F4F47DF314, + 0x001F9F04336BBE0A, 0x001F9CF12B79F9BC, 0x001F9AB84415ABC4, + 0x001F98555B782FB8, 0x001F95C3ABD03F78, 0x001F92FDA9CEF1F2, + 0x001F8FFCDA9AE41C, 0x001F8CB99E7385F8, 0x001F892AEC479606, + 0x001F8545F904DB8E, 0x001F80FDC336039A, 0x001F7C427839E926, + 0x001F7700A3582ACC, 0x001F71200F1A241C, 0x001F6A8234B7352A, + 0x001F630000A8E266, 0x001F5A66904FE3C4, 0x001F50724ECE1172, + 0x001F44C7665C6FDA, 0x001F36E5A38A59A2, 0x001F26143450340A, + 0x001F113E047B0414, 0x001EF6AEFA57CBE6, 0x001ED38CA188151E, + 0x001EA2A61E122DB0, 0x001E5961C78B267C, 0x001DDDF62BAC0BB0, +0x001CDB4DD9E4E8C0}; + +static const double we_double[] = { + 9.655740063209182975e-16, 7.089014243955414331e-18, + 1.163941249669122378e-17, 1.524391512353216015e-17, + 1.833284885723743916e-17, 2.108965109464486630e-17, + 2.361128077843138196e-17, 2.595595772310893952e-17, + 2.816173554197752338e-17, 3.025504130321382330e-17, + 3.225508254836375280e-17, 3.417632340185027033e-17, + 3.602996978734452488e-17, 3.782490776869649048e-17, + 3.956832198097553231e-17, 4.126611778175946428e-17, + 4.292321808442525631e-17, 4.454377743282371417e-17, + 4.613133981483185932e-17, 4.768895725264635940e-17, + 4.921928043727962847e-17, 5.072462904503147014e-17, + 5.220704702792671737e-17, 5.366834661718192181e-17, + 5.511014372835094717e-17, 5.653388673239667134e-17, + 5.794088004852766616e-17, 5.933230365208943081e-17, + 6.070922932847179572e-17, 6.207263431163193485e-17, + 6.342341280303076511e-17, 6.476238575956142121e-17, + 6.609030925769405241e-17, 6.740788167872722244e-17, + 6.871574991183812442e-17, 7.001451473403929616e-17, + 7.130473549660643409e-17, 7.258693422414648352e-17, + 7.386159921381791997e-17, 7.512918820723728089e-17, + 7.639013119550825792e-17, 7.764483290797848102e-17, + 7.889367502729790548e-17, 8.013701816675454434e-17, + 8.137520364041762206e-17, 8.260855505210038174e-17, + 8.383737972539139383e-17, 8.506196999385323132e-17, + 8.628260436784112996e-17, 8.749954859216182511e-17, + 8.871305660690252281e-17, 8.992337142215357066e-17, + 9.113072591597909173e-17, 9.233534356381788123e-17, + 9.353743910649128938e-17, 9.473721916312949566e-17, + 9.593488279457997317e-17, 9.713062202221521206e-17, + 9.832462230649511362e-17, 9.951706298915071878e-17, + 1.007081177024294931e-16, 1.018979547484694078e-16, + 1.030867374515421954e-16, 1.042746244856188556e-16, + 1.054617701794576406e-16, 1.066483248011914702e-16, + 1.078344348241948498e-16, 1.090202431758350473e-16, + 1.102058894705578110e-16, 1.113915102286197502e-16, + 1.125772390816567488e-16, 1.137632069661684705e-16, + 1.149495423059009298e-16, 1.161363711840218308e-16, + 1.173238175059045788e-16, 1.185120031532669434e-16, + 1.197010481303465158e-16, 1.208910707027385520e-16, + 1.220821875294706151e-16, 1.232745137888415193e-16, + 1.244681632985112523e-16, 1.256632486302898513e-16, + 1.268598812200397542e-16, 1.280581714730749379e-16, + 1.292582288654119552e-16, 1.304601620412028847e-16, + 1.316640789066572582e-16, 1.328700867207380889e-16, + 1.340782921828999433e-16, 1.352888015181175458e-16, + 1.365017205594397770e-16, 1.377171548282880964e-16, + 1.389352096127063919e-16, 1.401559900437571538e-16, + 1.413796011702485188e-16, 1.426061480319665444e-16, + 1.438357357315790180e-16, 1.450684695053687684e-16, + 1.463044547929475721e-16, 1.475437973060951633e-16, + 1.487866030968626066e-16, 1.500329786250736949e-16, + 1.512830308253539427e-16, 1.525368671738125550e-16, + 1.537945957544996933e-16, 1.550563253257577148e-16, + 1.563221653865837505e-16, 1.575922262431176140e-16, + 1.588666190753684151e-16, 1.601454560042916733e-16, + 1.614288501593278662e-16, 1.627169157465130500e-16, + 1.640097681172717950e-16, 1.653075238380036909e-16, + 1.666103007605742067e-16, 1.679182180938228863e-16, + 1.692313964762022267e-16, 1.705499580496629830e-16, + 1.718740265349031656e-16, 1.732037273081008369e-16, + 1.745391874792533975e-16, 1.758805359722491379e-16, + 1.772279036068006489e-16, 1.785814231823732619e-16, + 1.799412295642463721e-16, 1.813074597718501559e-16, + 1.826802530695252266e-16, 1.840597510598587828e-16, + 1.854460977797569461e-16, 1.868394397994192684e-16, + 1.882399263243892051e-16, 1.896477093008616722e-16, + 1.910629435244376536e-16, 1.924857867525243818e-16, + 1.939163998205899420e-16, 1.953549467624909132e-16, + 1.968015949351037382e-16, 1.982565151475019047e-16, + 1.997198817949342081e-16, 2.011918729978734671e-16, + 2.026726707464198289e-16, 2.041624610503588774e-16, + 2.056614340951917875e-16, 2.071697844044737034e-16, + 2.086877110088159721e-16, 2.102154176219292789e-16, + 2.117531128241075913e-16, 2.133010102535779087e-16, + 2.148593288061663316e-16, 2.164282928437604723e-16, + 2.180081324120784027e-16, 2.195990834682870728e-16, + 2.212013881190495942e-16, 2.228152948696180545e-16, + 2.244410588846308588e-16, 2.260789422613173739e-16, + 2.277292143158621037e-16, 2.293921518837311354e-16, + 2.310680396348213318e-16, 2.327571704043534613e-16, + 2.344598455404957859e-16, 2.361763752697773994e-16, + 2.379070790814276700e-16, 2.396522861318623520e-16, + 2.414123356706293277e-16, 2.431875774892255956e-16, + 2.449783723943070217e-16, 2.467850927069288738e-16, + 2.486081227895851719e-16, 2.504478596029557040e-16, + 2.523047132944217013e-16, 2.541791078205812227e-16, + 2.560714816061770759e-16, 2.579822882420530896e-16, + 2.599119972249746917e-16, 2.618610947423924219e-16, + 2.638300845054942823e-16, 2.658194886341845120e-16, + 2.678298485979525166e-16, 2.698617262169488933e-16, + 2.719157047279818500e-16, 2.739923899205814823e-16, + 2.760924113487617126e-16, 2.782164236246436081e-16, + 2.803651078006983464e-16, 2.825391728480253184e-16, + 2.847393572388174091e-16, 2.869664306419817679e-16, + 2.892211957417995598e-16, 2.915044901905293183e-16, + 2.938171887070028633e-16, 2.961602053345465687e-16, + 2.985344958730045276e-16, 3.009410605012618141e-16, + 3.033809466085003416e-16, 3.058552518544860874e-16, + 3.083651274815310004e-16, 3.109117819034266344e-16, + 3.134964845996663118e-16, 3.161205703467105734e-16, + 3.187854438219713117e-16, 3.214925846206797361e-16, + 3.242435527309451638e-16, 3.270399945182240440e-16, + 3.298836492772283149e-16, 3.327763564171671408e-16, + 3.357200633553244075e-16, 3.387168342045505162e-16, + 3.417688593525636996e-16, 3.448784660453423890e-16, + 3.480481301037442286e-16, 3.512804889222979418e-16, + 3.545783559224791863e-16, 3.579447366604276541e-16, + 3.613828468219060593e-16, 3.648961323764542545e-16, + 3.684882922095621322e-16, 3.721633036080207290e-16, + 3.759254510416256532e-16, 3.797793587668874387e-16, + 3.837300278789213687e-16, 3.877828785607895292e-16, + 3.919437984311428867e-16, 3.962191980786774996e-16, + 4.006160751056541688e-16, 4.051420882956573177e-16, + 4.098056438903062509e-16, 4.146159964290904582e-16, + 4.195833672073398926e-16, 4.247190841824385048e-16, + 4.300357481667470702e-16, 4.355474314693952008e-16, + 4.412699169036069903e-16, 4.472209874259932285e-16, + 4.534207798565834480e-16, 4.598922204905932469e-16, + 4.666615664711475780e-16, 4.737590853262492027e-16, + 4.812199172829237933e-16, 4.890851827392209900e-16, + 4.974034236191939753e-16, 5.062325072144159699e-16, + 5.156421828878082953e-16, 5.257175802022274839e-16, + 5.365640977112021618e-16, 5.483144034258703912e-16, + 5.611387454675159622e-16, 5.752606481503331688e-16, + 5.909817641652102998e-16, 6.087231416180907671e-16, + 6.290979034877557049e-16, 6.530492053564040799e-16, + 6.821393079028928626e-16, 7.192444966089361564e-16, +7.706095350032096755e-16, 8.545517038584027421e-16}; + +static const double fe_double[] = { + 1.000000000000000000e+00, 9.381436808621747003e-01, + 9.004699299257464817e-01, 8.717043323812035949e-01, + 8.477855006239896074e-01, 8.269932966430503241e-01, + 8.084216515230083777e-01, 7.915276369724956185e-01, + 7.759568520401155522e-01, 7.614633888498962833e-01, + 7.478686219851951034e-01, 7.350380924314234843e-01, + 7.228676595935720206e-01, 7.112747608050760117e-01, + 7.001926550827881623e-01, 6.895664961170779872e-01, + 6.793505722647653622e-01, 6.695063167319247333e-01, + 6.600008410789997004e-01, 6.508058334145710999e-01, + 6.418967164272660897e-01, 6.332519942143660652e-01, + 6.248527387036659775e-01, 6.166821809152076561e-01, + 6.087253820796220127e-01, 6.009689663652322267e-01, + 5.934009016917334289e-01, 5.860103184772680329e-01, + 5.787873586028450257e-01, 5.717230486648258170e-01, + 5.648091929124001709e-01, 5.580382822625874484e-01, + 5.514034165406412891e-01, 5.448982376724396115e-01, + 5.385168720028619127e-01, 5.322538802630433219e-01, + 5.261042139836197284e-01, 5.200631773682335979e-01, + 5.141263938147485613e-01, 5.082897764106428795e-01, + 5.025495018413477233e-01, 4.969019872415495476e-01, + 4.913438695940325340e-01, 4.858719873418849144e-01, + 4.804833639304542103e-01, 4.751751930373773747e-01, + 4.699448252839599771e-01, 4.647897562504261781e-01, + 4.597076156421376902e-01, 4.546961574746155033e-01, + 4.497532511627549967e-01, 4.448768734145485126e-01, + 4.400651008423538957e-01, 4.353161032156365740e-01, + 4.306281372884588343e-01, 4.259995411430343437e-01, + 4.214287289976165751e-01, 4.169141864330028757e-01, + 4.124544659971611793e-01, 4.080481831520323954e-01, + 4.036940125305302773e-01, 3.993906844752310725e-01, + 3.951369818332901573e-01, 3.909317369847971069e-01, + 3.867738290841376547e-01, 3.826621814960098344e-01, + 3.785957594095807899e-01, 3.745735676159021588e-01, + 3.705946484351460013e-01, 3.666580797815141568e-01, + 3.627629733548177748e-01, 3.589084729487497794e-01, + 3.550937528667874599e-01, 3.513180164374833381e-01, + 3.475804946216369817e-01, 3.438804447045024082e-01, + 3.402171490667800224e-01, 3.365899140286776059e-01, + 3.329980687618089852e-01, 3.294409642641363267e-01, + 3.259179723935561879e-01, 3.224284849560891675e-01, + 3.189719128449572394e-01, 3.155476852271289490e-01, + 3.121552487741795501e-01, 3.087940669345601852e-01, + 3.054636192445902565e-01, 3.021634006756935276e-01, + 2.988929210155817917e-01, 2.956517042812611962e-01, + 2.924392881618925744e-01, 2.892552234896777485e-01, + 2.860990737370768255e-01, 2.829704145387807457e-01, + 2.798688332369729248e-01, 2.767939284485173568e-01, + 2.737453096528029706e-01, 2.707225967990600224e-01, + 2.677254199320447947e-01, 2.647534188350622042e-01, + 2.618062426893629779e-01, 2.588835497490162285e-01, + 2.559850070304153791e-01, 2.531102900156294577e-01, + 2.502590823688622956e-01, 2.474310756653276266e-01, + 2.446259691318921070e-01, 2.418434693988772144e-01, + 2.390832902624491774e-01, 2.363451524570596429e-01, + 2.336287834374333461e-01, 2.309339171696274118e-01, + 2.282602939307167011e-01, 2.256076601166840667e-01, + 2.229757680581201940e-01, 2.203643758433594946e-01, + 2.177732471487005272e-01, 2.152021510753786837e-01, + 2.126508619929782795e-01, 2.101191593889882581e-01, + 2.076068277242220372e-01, 2.051136562938377095e-01, + 2.026394390937090173e-01, 2.001839746919112650e-01, + 1.977470661050988732e-01, 1.953285206795632167e-01, + 1.929281499767713515e-01, 1.905457696631953912e-01, + 1.881811994042543179e-01, 1.858342627621971110e-01, + 1.835047870977674633e-01, 1.811926034754962889e-01, + 1.788975465724783054e-01, 1.766194545904948843e-01, + 1.743581691713534942e-01, 1.721135353153200598e-01, + 1.698854013025276610e-01, 1.676736186172501919e-01, + 1.654780418749360049e-01, 1.632985287519018169e-01, + 1.611349399175920349e-01, 1.589871389693142123e-01, + 1.568549923693652315e-01, 1.547383693844680830e-01, + 1.526371420274428570e-01, 1.505511850010398944e-01, + 1.484803756438667910e-01, 1.464245938783449441e-01, + 1.443837221606347754e-01, 1.423576454324722018e-01, + 1.403462510748624548e-01, 1.383494288635802039e-01, + 1.363670709264288572e-01, 1.343990717022136294e-01, + 1.324453279013875218e-01, 1.305057384683307731e-01, + 1.285802045452281717e-01, 1.266686294375106714e-01, + 1.247709185808309612e-01, 1.228869795095451356e-01, + 1.210167218266748335e-01, 1.191600571753276827e-01, + 1.173168992115555670e-01, 1.154871635786335338e-01, + 1.136707678827443141e-01, 1.118676316700562973e-01, + 1.100776764051853845e-01, 1.083008254510337970e-01, + 1.065370040500016602e-01, 1.047861393065701724e-01, + 1.030481601712577161e-01, 1.013229974259536315e-01, + 9.961058367063713170e-02, 9.791085331149219917e-02, + 9.622374255043279756e-02, 9.454918937605585882e-02, + 9.288713355604354127e-02, 9.123751663104015530e-02, + 8.960028191003285847e-02, 8.797537446727021759e-02, + 8.636274114075691288e-02, 8.476233053236811865e-02, + 8.317409300963238272e-02, 8.159798070923741931e-02, + 8.003394754231990538e-02, 7.848194920160642130e-02, + 7.694194317048050347e-02, 7.541388873405840965e-02, + 7.389774699236474620e-02, 7.239348087570873780e-02, + 7.090105516237182881e-02, 6.942043649872875477e-02, + 6.795159342193660135e-02, 6.649449638533977414e-02, + 6.504911778675374900e-02, 6.361543199980733421e-02, + 6.219341540854099459e-02, 6.078304644547963265e-02, + 5.938430563342026597e-02, 5.799717563120065922e-02, + 5.662164128374287675e-02, 5.525768967669703741e-02, + 5.390531019604608703e-02, 5.256449459307169225e-02, + 5.123523705512628146e-02, 4.991753428270637172e-02, + 4.861138557337949667e-02, 4.731679291318154762e-02, + 4.603376107617516977e-02, 4.476229773294328196e-02, + 4.350241356888818328e-02, 4.225412241331623353e-02, + 4.101744138041481941e-02, 3.979239102337412542e-02, + 3.857899550307485742e-02, 3.737728277295936097e-02, + 3.618728478193142251e-02, 3.500903769739741045e-02, + 3.384258215087432992e-02, 3.268796350895953468e-02, + 3.154523217289360859e-02, 3.041444391046660423e-02, + 2.929566022463739317e-02, 2.818894876397863569e-02, + 2.709438378095579969e-02, 2.601204664513421735e-02, + 2.494202641973178314e-02, 2.388442051155817078e-02, + 2.283933540638524023e-02, 2.180688750428358066e-02, + 2.078720407257811723e-02, 1.978042433800974303e-02, + 1.878670074469603046e-02, 1.780620041091136169e-02, + 1.683910682603994777e-02, 1.588562183997316302e-02, + 1.494596801169114850e-02, 1.402039140318193759e-02, + 1.310916493125499106e-02, 1.221259242625538123e-02, + 1.133101359783459695e-02, 1.046481018102997894e-02, + 9.614413642502209895e-03, 8.780314985808975251e-03, + 7.963077438017040002e-03, 7.163353183634983863e-03, + 6.381905937319179087e-03, 5.619642207205483020e-03, + 4.877655983542392333e-03, 4.157295120833795314e-03, + 3.460264777836904049e-03, 2.788798793574076128e-03, + 2.145967743718906265e-03, 1.536299780301572356e-03, +9.672692823271745359e-04, 4.541343538414967652e-04}; + +static const double ziggurat_exp_r = 7.6971174701310497140446280481; + +/* Returns a standard uniform random variable */ +double +std_uniform() +{ + return (double) rand() / (double) ((unsigned) RAND_MAX); +} + +static uint64_t +rand_uint64(void) +{ + uint64_t r = 0; + + for (int i = 0; i < 64; i += 15) + { + r = r * ((uint64_t) RAND_MAX + 1) + rand(); + } + + return r; +} + +static double +standard_exponential_unlikely(uint8_t idx, double x) +{ + if (idx == 0) + { + /* Switch to 1.0 - U to avoid log(0.0) */ + return ziggurat_exp_r - log1p(-std_uniform()); + } + else if ((fe_double[idx - 1] - fe_double[idx]) * std_uniform() + fe_double[idx] < exp(-x)) + { + return x; + } + else + { + return random_standard_exponential(); + } +} + +double +random_standard_exponential() +{ + uint64_t ri; + uint8_t idx; + double x; + + ri = rand_uint64(); + ri >>= 3; + idx = ri & 0xFF; + ri >>= 8; + x = ri * we_double[idx]; + + if (ri < ke_double[idx]) + { + /* 98.9% of the time we return here 1st try */ + return x; + } + + return standard_exponential_unlikely(idx, x); +} + +/* Only for probabilities less than 0.33(3) */ +static long int +random_geometric_inversion(double p) +{ + double z = ceil(-random_standard_exponential() / log1p(-p)); + + /* + * The constant 9.223372036854776e+18 is the smallest double that is + * larger than INT64_MAX. + */ + if (z >= 9.223372036854776e+18) + { + return INT64_MAX; + } + + return (int64_t) z; +} + +#endif -- 2.52.0