From 09e7c7d9c255e2cda5eaf59fb0c5e1706cdfc69b Mon Sep 17 00:00:00 2001
From: LKedward <laurence.kedward@bristol.ac.uk>
Date: Sat, 21 Nov 2020 13:06:28 +0000
Subject: Add: simple string hashing functions

---
 fpm/src/fpm_strings.f90 | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/fpm/src/fpm_strings.f90 b/fpm/src/fpm_strings.f90
index a6511c9..3c64a08 100644
--- a/fpm/src/fpm_strings.f90
+++ b/fpm/src/fpm_strings.f90
@@ -1,9 +1,10 @@
 module fpm_strings
+use iso_fortran_env, only: int64
 implicit none
 
 private
 public :: f_string, lower, split, str_ends_with, string_t
-public :: string_array_contains, operator(.in.)
+public :: string_array_contains, operator(.in.), fnv_1a
 
 type string_t
     character(len=:), allocatable :: s
@@ -13,6 +14,11 @@ interface operator(.in.)
     module procedure string_array_contains
 end interface
 
+interface fnv_1a
+    procedure :: fnv_1a_char
+    procedure :: fnv_1a_string_t
+end interface fnv_1a
+
 contains
 
 logical function str_ends_with(s, e) result(r)
@@ -48,6 +54,46 @@ function f_string(c_string)
 end function f_string
 
 
+!> Hash a character(*) string of default kind 
+pure function fnv_1a_char(input, seed) result(hash)
+    character(*), intent(in) :: input
+    integer(int64), intent(in), optional :: seed
+    integer(int64) :: hash
+
+    integer :: i
+    integer(int64), parameter :: FNV_OFFSET_32 = 2166136261_int64
+    integer(int64), parameter :: FNV_PRIME_32 = 16777619_int64
+
+    if (present(seed)) then
+        hash = seed
+    else
+        hash = FNV_OFFSET_32
+    end if
+
+    do i=1,len(input)
+        hash = ieor(hash,iachar(input(i:i),int64)) * FNV_PRIME_32
+    end do
+
+end function fnv_1a_char
+
+
+!> Hash a string_t array of default kind 
+pure function fnv_1a_string_t(input, seed) result(hash)
+    type(string_t), intent(in) :: input(:)
+    integer(int64), intent(in), optional :: seed
+    integer(int64) :: hash
+
+    integer :: i
+
+    hash = fnv_1a(input(1)%s,seed)
+
+    do i=2,size(input)
+        hash = fnv_1a(input(i)%s,hash)
+    end do
+
+end function fnv_1a_string_t
+
+
 elemental pure function lower(str,begin,end) result (string)
     ! Changes a string to lowercase over specified range
     ! Author: John S. Urban
-- 
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